An Indian will chase a thing till he thinks he's chased it enough. Then he quits.
9 seconds sound clip from the The Searchers (1956) movie soundboard.
You can hear this line at 00:43:24 in the Blu-ray version of the movie.
Quote context
[...]
- Why don't you say it? We're beaten, and you know it.
- No. Our turnin' back don't mean nothin'. Not in the long run.
- For a while, they'll keep her and they'll raise her as one of their own until she's of an age to...
- Do you think maybe there's a chance we still might find her?
- An Indian will chase a thing till he thinks he's chased it enough. Then he quits.
[...]