Humans can recognize tyranny but never do anything about it. Bullying, abusive relationships, and slavery are some examples of this reality. Once you recognize the form of tyranny, you can put a name to it and act.
I don't know the exact reasons people put up with tyranny. I suspect every situation is somewhat unique. However, answering that question would allow many future harms to be prevented.
The American revolutionaries declared King George III a tyrant, but that couldn't be the end; open rebellion would mean certain harm or death. So, they acted. They made a case for taking up arms against the crown. They then resolved to become independent (found in the Lee Resolution/"Resolution of Independence"). Two days later, they declared independence. And they fought. Note, though, that the Revolution required the recognition of tyranny.