聞くは一時の恥、聞かぬは一生の恥 (きくはいっときのはじ、きかぬはいっしょうのはじ): better to ask and be embarrassed than not ask and never know

better to ask and be embarrassed than not ask and never know

Asking is a moment of shame, not asking is a lifetime of it. The line to quote at anyone sitting on a question because they feel they should already know the answer.

A Japanese proverb (ことわざ)