Arrow, Season 1

Arrow:
Your father's been poisoned. An assassin named Floyd Lawton laces his bullets with curare. I've dealt with this before. We need to dilute the poison in bloodstream.

Tommy:
I said stay the hell back!

Arrow:
In three minutes he's paralyzed. In four minutes, he suffocates. If you don't let me help you now, he's dead before anybody gets here!

Tommy:
Help. How?

Arrow:
Fresh blood buys him time to get to the hospital.

Tommy:
A blood transfusion? That's insane!

Arrow:
It's the only way. He needs your blood. You're out of time. You need to make a decision right now.

Tommy:
Why should I trust you?

Oliver:
[pulls off his hood showing his face to Tommy] Because you always have.