expression
needn't have done; shouldn't have done; better left undone
Archaic expression conveying that an action was unnecessary or regrettable. Modern equivalents include しなくてよかった or するべきではなかった.
「やらずもがなのことをしてしまった」と、昔の人は言ったものだ。
People in the old days would say, 'I ended up doing something I shouldn't have done.'