Jamieson, Fausset and Brown on Ecclesiastes 7:17

17. over much wicked--so worded, to answer to "righteous over much." For if not taken thus, it would seem to imply that we may be wicked a little. "Wicked" refers to "wicked man" (Ec 7:15); "die before thy time," to "prolongeth his life," antithetically. There may be a wicked man spared to "live long," owing to his avoiding gross excesses (Ec 7:15). Solomon says, therefore, Be not so foolish (answering antithetically to "over wise," Ec 7:16), as to run to such excess of riot, that God will be provoked to cut off prematurely thy day of grace (Ro 2:5). The precept is addressed to a sinner. Beware of aggravating thy sin, so as to make thy case desperate. It refers to the days of Solomon's "vanity" (apostasy, Ec 7:15), when only such a precept would be applicable. By litotes it includes, "Be not wicked at all."