Quoting Theo Seeds:

smart people have a bigger “bag of tricks” for justifying the stupid bullshit they believe. It’s easier for them to come up with a convincing explanation for believing something dumb. So they’re less likely to realize they’re wrong.

The problem is, if you’re constantly thinking about everything that can go wrong, it messes with your brain. You won’t take as many risks, because you’ll be way more afraid. That means you won’t do as much stuff and you won’t be effective in the real world.
It’s better to just not worry about the bad stuff that can happen, and enjoy life.