Enemy Reactions. Enemies have different reactions when you get in their range. Some enemies will attack you on sight as long as they are close to your level or a higher level than your party. Some enemies are nuetral and only attack if attacked first. Some enemies will attack even if neutral if you attack another enemy of its kind. There are also some enemies that are blind and you have to sneak by because they attack by sound.
There is a symbol on each enemy's nameplate that indicates their reaction. In the image, you can see an eye symbol which means if the enemy is in your level range, it will attack you when it sees you.