The phrase "huge mistake" means an error or blunder that is very significant, serious and has severe consequences. It refers to a decision or action that turned out to be wrong, resulting in negative results or repercussions. The magnitude of the mistake could have been due to carelessness, lack of knowledge, misjudgment or any other reason, but it had major implications. In short, "huge mistake" is an expression used to describe a serious error that has caused harm or damage in some way.