Free Choice & the Yetzer Hara

A person is in constant battle with the yetzer hara by necessity—to overcome it by choosing good and doing what God wants. Every time you kill your yetzer hara through performing some holy action, you get a brand new yetzer hara corresponding to your higher level. In this way, your free choice is not nullified. (Reb Gedaliah Aharon Kenig, Shaarei Tzaddik, Letter #41)