A small, background fear of screwing up is wise, as long as it's not preventing you from what you should be doing for "normal" flying. After 43 years of flying, I can occasionally still feel the little fear of screwing up in the background, I listen to it, and it keeps me sharp. I've helped a lot of pilot friends who have screwed up, and attended a number of funeral, including one last week. So reminding yourself to be cautious has it's merits, just don't let it paralyze you...