In season 1, Peter Campbell tries to blackmail Draper into giving him the job of head of accounts by using his secret past against him. Draper refuses to budge, and Peter's plan backfires when their boss Cooper doesn't seem to care about Draper's past. When Peter leaves, Cooper gives Draper his blessing to fire Peter (in contrast with him protecting Peter the last time Draper wanted to fire Peter). Yet Draper doesn't. I've never understood his reasoning for it. Why didn't Draper fire this person who is so openly antagonistic to him?
Note: I've only seen season 1 and part of 2 so far.