system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What causes revolutions? How bad do things have to get before such a large number of people agree on how bad things are and come together to fix it?

We hear politicians make promises during their campaigns, yet it seems that even though hardly any of those promises are kept, people don't really hold them accountable. However, there obviously have been times when the people get fed up enough and start a revolution. How come something like this hasn't happened to hold politicians accountable for their promises? How bad does it have to get?
gpt
One big condition is common knowledge. In many cases, each individual feels that things are rotten, but worries that they are the only ones who feel that way. It's when something big happens that makes everyone realize the majority feels things are rotten that a lot can get done.