He that sings on Friday shall weep on Sunday.

This saying holds that a burst of cheerfulness may be followed, before long, by grief. Setting singing on one day beside weeping two days later pairs joy with sorrow, as though happiness hinted that a reversal was close at hand.

It describes a sequence of changing fortunes or feelings rather than a lesson about conduct. The saying gives no reason for the sorrow and lays no blame on the singer; its superstitious note is a wary suggestion that high spirits may not last.

Use it when sudden merriment prompts a half-serious, superstitious warning that sadness may soon follow, or when recalling a happy moment that quickly gave way to grief. It presents the change as a familiar pattern, not as punishment or as proof that singing causes or deserves weeping.