There are lots of reasons to be unhappy with a regime, but only undermined legitimacy will provoke a revolution.
Fights for legitimacy capture ancient instinct driven responses in people that go back all of the way to our hunter and gatherer days. We are hard wired to respond to leadership disputes in very particular ways.
Even very, very bad regimes (e.g. North Korea during its worst famines, Albania) won't face revolutions if the regime's legitimacy and authority is not seriously subject to question.
There is a myth that revolutions are caused by mismanagement of government, but, in general, that is not true. It takes not just disagreements on matters of policy and/or bad results, but a perception that the current regime is insane or controlled by outside conspirators or has engaged in impermissible corruption against its purported values, to make a regime or leader ripe to be replaced.
Regimes are more vulnerable to revolutions when the regime is not well established yet, are more vulnerable where they is a succession dispute or disputed election, are more vulnerable to revolution when ideas like "democracy" delegitimize the hereditary or other basis of the existing regime, are more vulnerable when regime leaders appear to defy or disregard the basis (religious, legal, or otherwise) that justifies their authority.
2. Revolutions are normally led by secondary elites in the existing regime.
To present a viable alternative to the status quo there need to be people who are suitable to serve as leaders of a new regime, particularly if they have been somehow slighted relative to their perceived entitlement. Even if the mass of the revolution is run by the masses, the revolution will usually be lead by young military officers, university students, union leaders, religious leaders, or disaffected aristocrats who won't be getting inheritances because they are younger children.
For example, when new political parties that turn out to be viable are formed and replace some existing major political party, the leadership of the new political party almost always includes experienced politicians of repute who have defected from their prior political party affiliations.
3. Revolutions need to create a sense of identity in the revolting population.
An ethnic or "national" identity can be particularly effective in this regard but isn't the sole available identification. Revolutions basically harness tribal instincts and are most effective when a "tribe" feels like it doesn't have any meaningful way to receive a fair shake through the status quo. One of the reasons that ISIS was able to take so much land so quickly in Iraq and Syria was that neither the Iraqi government, nor the Syrian government, both of which were dominated by non-Sunni Arab factions, seemed to provide a meaningful voice for Sunni Arabs.
It doesn't really matter if the policy differences for the "oppressed" tribe are really all that substantive, indeed symbolic differences are probably more powerful. Instead, what matters is an appearance of having no advocates for your "tribe" in the current regime.
Social class, if clearly enough delineated and felt by people can form a basis for a revolution, but if it is divorced from an ethnic identity, it is less likely to. For example, even though the economic interests of whites in Appalachia and blacks in the United States have lots of similarities, the lack of a shared ethnic identity has prevented them from forming viable coalitions with each other in the past few decades.
Even an oppressive caste or slavery system can be quite stable, so long as the legitimacy of the system is not cast into doubt, the oppressed "tribe" has no one to lead them from the elite, or it is hard for the oppressed population to see itself as not part of the same social and political system as their oppressors.
Religious affiliations can be a powerful way to create a sense of "tribal" identity and a source of crystalized sense of membership in an ethnicity which often tracks religious affiliation anyway, although these are hardly the exclusive means by which this can be accomplished.
4. Revolutions need a spark.
It can be almost anything - a woman refusing to take her designated place on a city bus, a single incident of police brutality, or an incident that victimizes a member of the revolting tribe that is viscerally humiliating or disgusting in a way the causes other to feel empathy.
But, without a triggering spark that creates a unified emotional reaction, the masses that need to rise up in a coordinated matter won't be able to mobilize. Contrawise, a good spark can trigger the early phase of a revolution even without much organization on the part of would be leaders, although it will only keep burning instead of puttering out if the other elements of a successful revolution are present.
5. Revolutions need to be mishandled by those in power.
If the existing regime can find a way to promptly defuse the revolutionary movement, it will die. Crushing early revolutionaries without mercy can also be effective if this successfully creates the appearance among the revolting populace that they are hopelessly outmatched. Thus, the regime must either demonstrate that it doesn't deserve to be the subject of a revolution (or that there are viable alternatives like political campaigns through ordinary channels to a revolution), or convince potential revolutionaries that it is hopeless to try, or both.
6. Revolutions need resources.
Successful revolutions, unlike unsuccessful revolutions that start but don't follow through, need a logistical basis of funds and personnel. It can be foreign or domestic.
Economics can drive this by creating a class of overqualified and underemployed people with the time necessary to commit to the cause and little to lose. A failure to co-opt almost everyone who is competent to lead a revolution or even simply to work in it as a follower, is a common failing of a regime that creates conditions ripe for revolution. For example, a lot of Islamic revolutionary action is driven by huge numbers of young unemployed men with theology degrees in Saudi Arabia in large families who have no way to prove their own worth and lots of time on their hands, freedom and a sense of privilege.
The labor movement thrived when competent people were kept out of management by accident of birth, and deflated when more meritocratic grounds for advancement plucked the most qualified potential union leaders into the ranks of management, both directly by depriving unions of resources and indirectly by creating a perception of opportunity that those who advanced from lesser conditions by virtue of merit created when they filled leadership positions.
A subset of this is religious backing. Religions thrive when they provide a cultural center for a threatened or oppressed culture, and wither organizationally when their creeds merely replicate the status quo establishment position. People back religions actively and with resources because they think this support is necessary for their culture to survive.
7. Revolutions need to inspire self-sacrifice.
Some of those personnel need to perceive the cost as just enough for it to be heroic to die for it, or at least to take great risks of ruin for it beyond personal advantage. Unless some key figures in the revolutionary movement see their efforts as advancing the greater good of a worthy cause, the revolution will fail.
Religiously based revolutions are often good at inspiring self-sacrifice, but religious revolutions have no monopoly on this and fear of a theocracy from a regime can be just as effective in many cases at inspiring this. Still, there needs to be something that some true believers can sincerely hold onto as being worthy of self-sacrifice without question.
8. Revolutions can easily fall into stalemate mode.
The more time passes, the less likely the insurgency is to be resolved finally for either party. Many revolutions and coups are swiftly successful or fail just as swiftly; but very long standoffs where the revolutionaries don't have the capacity to replace the regime in the near future, but the regime doesn't have the capacity to end the insurgency are common and can last for decades. Even 5% or 10% of the population that is absolutely convinced that the current regime is illegitimate is enough to keep a revolution going indefinitely, but that is not enough support to bring about a change in control. Regimes don't need mass agreement with their policies to succeed, but they need nearly uniform (certainly more than 99%) belief in their legitimacy to avoid a prolonged and difficult to manage insurgency.
9. Revolutions need to convince people that their conditional support will pay off.
While every revolution has die hard supporters on each side, lots of people are contingent and conditional supporters of whichever side that they perceive will prevail who are trying to act in their own best interests in a confusing time.
The appearance of a likelihood of success can dramatically chance the tides of an uprising, as the recent attempted coup in Turkey illustrated. The President's ability to access mass media and convince people that he was alive and in control caused lots of people to mobilize in support of his regime and to remain silent as he ruthlessly consolidated control.
The perception that you can win is as importance as the reality. This is why control of communication channels is so important during revolutions - it affects people's perceptions.
10. A revolution's leaders need to have enough of a vision to act decisively until things settle down.
A revolution, should it achieve temporary control has a brief honeymoon period, like any new regime, during which it has to show that it is in control and bringing about sweeping change that benefits the winners of the revolution and justified the cause. An appearance of incompetence, corruption, or lack of direction and vision and change, can open the door to a swift and successful counter-revolution by old regime elements who can show that they know what they are doing and what needs to be done, while disavowing the most abhorrent acts or individuals of the old regime.
11. Revolutions can happen at any scale.
A revolution can involve changes in group leadership at any level that is or can be made to become sovereign (i.e. accountable to no one above them in all material things in the near term) from a group of cast aways on an isolate or group of POWs in a camp, all the way up to whole nations or even groups of nations.
But, revolutions do not generally happen at any level that is less than sovereign, because subordinate units in a hierarchy that don't claim to be sovereign can almost always have any legitimacy or succession dispute resolved by those who are higher up in the hierarchy that it is a part of.
12. Revolutions tend to come in waves.
A strategy sufficient to undermine the legitimacy of one regime will often have a contagion effect and spread to other similar regimes (a la Arab Spring, the Revolutions of 1848, the Revolutions of the late 1800s that removed monarchies, created national identities and drove Latin American independence movements, the Communist wave of revolutions, the post-colonial independence movements).
These larger waves provide intellectual fuel to undermine legitimacy, economic and personnel support and training, a model for creating tribal identity, and by the success of the early versions of the attempt give hope for those following them that it is viable.
This hope is often misfounded as the homegrown version of the revolution is often more solidly organized, well planned, and tuned to local conditions to an extent often not recognized (unless the general approach is revised substantially for local conditions as Mao did for Stalinism). But, it still creates hope and people often don't look very critically at the prior revolutions about which they are often ill informed anyway in deciding to make conditional and contingent commitments to the revolution that are critical to its success.