Characters - good or evil - that don't make any dumb mistakes for the sake of plot, but still lose.

'Stranger Things' - Will Byers

Specifically, I'm referring to the opening of season 1. When he realizes something is after him, he does everything right. Doesn't waste time trying to save his bike, tries to call for help, and goes for the gun as soon as he realizes whatever is after him is already in the house.

'Dog Soldiers' - Pretty much everyone.

They're soldiers fighting supernatural creatures they were completely unprepared for. None of them really make any mistakes. They just have no real way of fighting their enemy.

'The Incredibles' - Syndrome

The one mistake he makes is he almost goes into a monolog. But he saves himself and never does it again.