From The Treasure of the Sierra Madre
Aah, gold's a devilish sort of thing, anyway. You start out, you tell yourself you'll be satisfied with 25,000 handsome smackers worth of it. So help me, Lord, and cross my heart. Fine resolution. After months of sweatin' yourself dizzy, and growin' short on provisions, and findin' nothin', you finally come down to 15,000, then ten. Finally, you say, "Lord, let me just find $5,000 worth and I'll never ask for anythin' more the rest of my life."
$5,000 is a lot of money.
Yeah, here in this joint it seems like a lot. But I tell you, if you was to make a real strike, you couldn't be dragged away. Not even the threat of miserable death would keep you from trying to add 10,000 more. Ten, you'd want to get twenty-five; twenty-five you'd want to get fifty; fifty, a hundred. Like roulette. One more turn, you know. Always one more.