Because one focuses his training on speed, while the other focuses more on accuracy.
He can. It's called critical hit. Also, he could have any other source of advantage than being hidden, or be a swashbuckler.Why does a rogue always strike for substantial damage only when he's hidden or an enemy is standing next to his opponent, can't he get lucky?
They don't. Turns and rounds only exist for the player's convenience, in fiction, the actions are simultaneous.Why do PCs sit there and watch enemies stab their unconscious friend, only leaping into action when its their 'turn'?