Once bitten, twice shy
Definition 1 of 1
Pro Tip 1/3Emotional Impact
The phrase often implies strong feelings from a past negative experience affecting current behavior. 
He no longer rides motorcycles; once bitten, twice shy.
Pro Tip 2/3Not Literal
It's a metaphorical expression. No actual biting is involved; it refers to any kind of bad experience. 
After a painful breakup, she stopped dating—once bitten, twice shy.
Pro Tip 3/3Common Usage
Used to suggest someone has become more cautious due to a previous negative outcome. 
He double-checks all his work now; once bitten, twice shy.