The only one I beat myself up over is hanging on to options too long, since that was greed. The other decisions were all reasonable given what I knew at the time.
I think it doesn't have to be all or nothing, it could also be possible to have a balanced approach to this problem. If your options start to be worth quite a bit more than your buy in price (eg: 2x), you can exercise some percentage of them but keep the rest. People more vested in investing would probably say that the ideal strategy would involve picking some thresholds ahead of time. Either way, there's always some amount of luck in this. The amount of things you don't know is a lot larger than what you do know. You may also not be in the right financial position to invest when a great opportunity shows up.
If it makes you feel any better, I did exactly the same thing: failed to exercise my options, lost out on six figures. Not the hugest payday but it would have been life-changing at the time. Such is life.
It would be entertaining[1] to know what proportion of "paper millionaires" in the field do hang on to the money and could retire to the Turks and Caicos. Also what proportion of valley employees become paper millionaires in the first place.
[1] And I mean entertaining because I'm in a bizarrely cynical mood this morning.