If someone falls or goes to pieces, that person becomes unable to think clearly and control their emotions because of something unpleasant or difficult that they have experienced.

She just went (all) to pieces during finals. 她考试时脑子里一团糟。

to break apart into smaller parts

The glass must have been cracked - it just fell to pieces in my hand. 玻璃杯肯定有裂缝——到我手上就碎了。

His clothes were dirty and falling to pieces. 他的衣服又脏又破。

If a relationship, organization, or system falls or goes to pieces, it fails.

Their marriage began to fall to pieces after only a few months. 才过了几个月，他们的婚姻就开始走下坡路了。