The stories we tell ourselves
Here's one: "I'm too old to make a difference, take a leap, change the game..." (Sometimes, I hear this from people who are 27 years old).
This is a seductive story, because it lets us off the hook. Obviously, the thinking goes, the deck (whichever deck you want to pick) is stacked against me, so no need to even imagine the failure that effort will bring. Better to just move along and lower my expectations.
Hannes Schwandt has published some interesting research on this. Regret seems to peak at 50, and then, as people start rationalizing that they're not expected to make much of a difference going forward, life satisfaction starts to increase. Of course, this is doubly backwards... we can (and must) contribute as we get older, and freedom is nothing to fear.