Another common one, is you hold a big equity position, but get pushed out/leave early long before there is an exit event. The investors and executives still at the company will fuck you over on your options, and like diluted your options after you left. This happens literally all the time, and if you arent the CEO, there is almost nothing you can do.

Just a few weeks ago, I met a CTO that got the company to a series A level of revenue, by building the whole product over two years. Was fired by the CEO, who brought on new investors, recapped the equity table, and drove his option value to almost nothing.