"The nightmares? They never go away, Snake. Once you’ve been on the battlefield, tasted the exhilaration, the tension… it all becomes part of you. Once you’ve awakened the warrior within… it never sleeps again. You crave ever bigger tensions, ever bigger thrills. As a mercenary, I’d think you would have realized that by now. You care nothing for power, or money, or even sex. The only thing that satisfies your cravings is war! All I’ve done is give you a place for it. I’ve given you a reason to live."
Big Boss - Metal Gear 2: Solid Snake