Unless you're involved with thinking about what you're doing, you end up doing the same thing over and over, and that becomes tedious and, in the end, defeating.
“I get anxious about a lot of things, that's the trouble. I get anxious about everything. I just can't stop thinking about things all the time. And here's the really destructive part - it's always retrospective. I waste time thinking of what I should have said or done.”