give someone enough rope to hang themselves
give (one) enough rope to hang (oneself)
To give one the opportunity to do something wrong or detrimental to oneself, because one will usually do it. The saying expresses the belief that someone does not need to interfere to bring about one's downfall. Don't interrupt him with questions. Just let him keep talking and he'll incriminate himself. Give him enough rope to hang himself!
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
give someone enough rope to hang themselvesor
give someone just enough rope to hang themselves
If you give someone enough rope to hang themselves or give someone just enough rope to hang themselves, you give them the freedom to do something in the way they want to, because you know that way they are likely to fail. I gave him enough rope to hang himself. I let him make the decision, knowing that it would be the wrong one, and then just watched the chaos that followed. Note: People sometimes use the shorter expression give someone enough rope or give someone just enough rope. I started to wonder if was all part of their great plan — give me just enough rope.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012