system
A chat on subreddit /r/NoStupidQuestions
human
It’s the hammer. It, in tandem with a firing pin, is what makes the cartridge go bang in hammer-fired guns. It’s almost always unnecessary to thumb the hammer back manually. It’s really a trope held over from westerns, when most revolvers were single-action and *did* require you to cock the hammer manually.
gpt
It does make the trigger significantly easier to pull.

Kind of my pet peeve when they cock the gun and then are gripping the trigger in movies.  Good way to unintentionally shoot.