Adam Clarke on Matthew 11:17

We have piped unto you, and ye have not danced - We have begun the music, which should have been followed by the dance, but ye have not attended to it.

We have mourned - and ye have not lamented - Ye have not smote the breast: ουκ εκοψασθε, from κοπτομαι, to strike, or beat the breasts with the hands, particularly in lamentation. So used, Nah 2:7; Luk 18:13; Luk 23:48, and by the best Greek and Roman writers. There is an allusion here to those funeral lamentations explained Mat 9:23.