One rotten apple can spoil the whole barrel.
4 seconds sound clip from the Bronco Billy movie soundboard.
You can hear this line at 01:38:11 in the Blu-ray version of the movie.
Quote context
[...]
- Mmm, smell that fresh morning air. Look at the blue sky above.
- You been drinking doc's snakebite?
- I know you think I've brought bad luck to the show.
- I'll shoot straight with you, Miss Lily. You have.
- One rotten apple can spoil the whole barrel.
- I've been like a scared little calf in a herd.
- Look, a man's got to prove himself on the range. That holds for a woman.
- Could we have a cup of coffee?
- I will.
[...]