Scientist Erica Chenoweth, who studies civil resistance at Harvard Kennedy School in Cambridge in the U.S., showed that every movement that mobilized at least 3.5% of a population was successful. This led to what’s known as the 3.5% rule — that protests require this level of participation to ensure change.

But the figure can be misleading, Chenoweth cautions. A much larger number of people are probably supporting a successful revolution even if they aren’t visibly protesting.