Comprehensive resource for understanding and mastering English idioms
The idiom "break down" means to cause or make someone feel tears, to be angry or upset, or to lose control of one's emotions. It can also mean to analyze or examine something in detail, or to physically break something into smaller pieces.
The idiom "break down" has been used since at least the 16th century. It originally meant to physically break something into smaller pieces, but over time its meaning has shifted to include emotional breakdowns as well. The phrase may have originated from the idea of breaking something apart or taking it apart in order to understand it better.