One of my favourite movie lines comes from a western called "Ulzana's Raid". A young cavalry officer is desperate to chase after a band of renegade Apaches. The wise old scout, played by the brilliant Burt Lancaster, responds drily.
"An Apache steals a horse and rides it till it falls down. Then he lights a fire under it to get it going again. Next time it falls down, he shoots it, eats it and steals another one. Ain't no way we're gonna beat that."
That's the gist of it, anyway, and it's a great line.