不自量力------go beyond one's depth

例句：
A: He tries to challenge the world champion boxer.
他企图向世界拳击冠军挑战。
B: If he does so, he really goes beyond his depth, for the champion is never defeated.
如果他如此做的话，他的确不自量力，因为那 冠军从未被击败过。

同义词：
bite off more than one chews
overreach oneself
throw straws against the wind