Halakhah su Ecclesiaste 7:26

He prohibited us that we not wander after our hearts to the point that we believe doctrines that are the opposite of the doctrines that the Torah obligates us. Rather we must restrain our thoughts and place a boundary against them to stand thereby - and that is the Torah's commandments and its prohibitions. And that is His saying, "and you shall not wander after your hearts and after your eyes" (Numbers 15:39). And the language of the Sifrei (Sifrei Bamidbar 115:1) is, "'After your hearts' - that is heresy, as the matter that is stated (Ecclesiastes 7:26), 'And I find more bitter than death the woman (understand to mean heresy), etc.' 'And after your eyes' - that is promiscuity, as the matter that is stated (Judges 14:3) 'Take her for me, for she is just in my eyes.'" [This is] meaning to say, being drawn after physical desires and mental involvement with them. (See Parashat Shelach; Mishneh Torah, Foreign Worship and Customs of the Nations 2.)