give one enough rope and he will hang himself
Give a bad person enough time and freedom to do as he pleases, and he may make a bad mistake or get into trouble and be caught. — A proverb.
Johnny is always stealing and hasn't been caught. But give him enough rope and he'll hang himself.
- Often used in a short form, "give one enough rope".
Mother didn't know who robbed the cookie jar, but she thought she could catch him if she gave him enough rope.
Source: A Dictionary of American Idioms