“自不量力”，亦作“不自量力”，意思是自己不估量自己的能力，指过高地估计自己的力量（overestimate one's own strength or ability），与英文谚语“bite off more than one can chew”意思相近，表示“to take (on) more than one can deal with; to be overconfident”。

例句：

我本应该小心，但是我自不量力。下来的时候我几乎立即失去控制，结果撞到一棵树上受伤了。

Instead of being cautious, I bit off more than I could chew. On my way down, I lost control almost immediately and slammed into a tree and got injured.

你得小心，不要自不量力。

Be careful you don't bite off more than you can chew.