To prepare for any event or crisis that may occur. My dad is nervous about me driving so far on my own, so I'm sure he's screwed himself up to concert pitch and is stationed by the phone in case I call.

To give one the opportunity to do something wrong or detrimental to oneself, because one will usually do it. The saying expressess 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!