μὴ κακὸν εὖ ἔρξῃς· σπείρειν ἴσον ἔστ' ἐνὶ πόντῳ → do no good to a bad man; it is like sowing in the sea
P. and V. ἀγνώμων, πικρός, σχέτλιος, σκληρός, Ar. and P. χαλεπός; see cruel.