千不该万不该

千不该万不该

Literally means:

thousand shouldn't, million shouldn't

Actually means:

deeply regret; should never have done sth

千 (thousand), 万 (ten thousand), here are both imaginary figures.

The phrase indicates one should never have done something, or something should never have happened, implying that one is regretful.

千、万，在这里都不是实在的数目，是表示强调。

千不该万不该，非常不应该，实在不应该。强调不应该做某事，或发生某事。