I'm constantly doubting myself over whether I rely too much on experimentation vs sitting down and figuring things out.
When I go through a bunch of tests to figure out what's going on, I worry that if I were more intelligent, I'd be able to reason about code and not need to try things as much, saving a bunch of time.
Contrariwise, when I am deep in code trying to figure things out, I worry that I'm taking too much time trying to deduce things when I could save time and do an experiment or three.