Skyscraper
Adventurer
You're a Fighter. Let's say Sword-and-Shield. You have trained in the Guardian School. You know you're tougher than your allies, and better defended, and you can't bear to imagine standing there, at the end of the fight, cowering behind your shield while they're dead.
But, as I say, you're trained in the Guardian School, Mamorujutsu, a martial art that uses a blade to defend your allies.
You want the enemy dead, or at least not fighting anymore. So, you go up to one of them, a sneaky looking bugger with a rapier, and you "mark" him: you watch him, paying attention to his every movement.
The moment he takes his eyes off you, BAM! you strike at his exposed flank.
He turns back to you, and you clash swords. He's learnt his lesson now, he never turns away from you.
You're not worried about your own safety, you'll be fine. You've got your armour, your sword, your shield. You can take a few hits.
But William the Wizard? He's a good guy, really, his spells really help in a fight, you love him to bits. Without him, you'd eventually be over-run by sheer numbers.
But he's a nerd, with a book, wearing robes. If this bugger got to him he'd only last a few seconds.
So you stand here, and you guard him while he prepares his spells, and blasts through the enemies.
Interesting explanation.