Eat humble pie
Definition 1 of 1
Pro Tip 1/3Admission of Error
It signals recognizing one's own mistake or poor judgement, not just experiencing bad outcomes. 
I had to eat humble pie after my plan caused the team to fail.
Pro Tip 2/3Humility Required
The phrase implies that the speaker feels genuine regret and is being sincere in their contrition. 
The CEO ate humble pie during the press conference, apologizing for the oversight.
Pro Tip 3/3No Literal Meaning
It is metaphorical and has nothing to do with eating actual pie; 'humble' relates to being humble. 
After mocking the amateur player, the pro had to eat humble pie when he was defeated.