It's not what people do that matters, it's why they do it.

«This is why I run.»
Because caring was a thing with claws. It sank them in, and didn't let go. Caring hurt more than a knife to the leg, more than a few broken ribs, more than anything that bled or broke and healed again. Caring didn't break you clean. It was a bone that didn't set, a cut that wouldn't close.
It was better not to care - Lila tried not to care - but, sometimes, people got in. Like a knife against armor, they found the cracks, slid past the guard, and you didn't know how deep they were buried until they were gone and you were bleeding on the floor. And it wasn't fair.

Young people like to think they're invincible. They don't like to face any situation where they've gotten weaker instead of stronger.

It's always hard, when introducing readers to a new world/set of rules, not to lay it all out manual-style in the opening chapters but make sure to put the action and the characters at the front. If people don't become invested in them and in the story, the world in which it's set will become a burden.

So many people think that if you're writing fantasy, it means you can just make everything up as you go. Want to add a dragon? Add a dragon! Want some magic? Throw it in. But the thing is, regardless of whether you're dealing with realism or fantasy, every world has rules. Make sure to establish a natural order.

Fencing is a game of living chess, a match where reflexes only work in combination with intent, and mind and body must work together at every moment.