Asklemmy

One of the hardest questions humans have ever asked. I can tell you though, that we decide it. Each individual ultimately chooses it for themselves. They can choose to go with what person A said, or person B, or something they came up with themselves. The choice is theirs though, this is just free will.

This is part of what makes the world so messy, because people pick different things. An extremist religious militant may pick something very different from some doctor volunteering to work in impoverished or war-torn areas.

Hashing these things out tends to come in during your later school years, since it can get really complicated in different ways sometimes, and a capable professional needs to be ready for that.

It gets calculus-levels of hard-to-figure-out sometimes though, which film, tv and games all usually ignore because it's not fun enough. It actually sucks gigantic donkey balls, when you run into a nasty, complicated moral problem. Not fun at all, and the world is full of them.