R' Shimon ben Menasya says: What is [referred to as] a twisted thing cannot be made straight? One who has an illicit relation-ship and begets a mamzer. Were you to say that [the reference is to] one who steals or robs [this could not be the meaning since] he can make restitution and [thus] make it straight.  R' Shimon ben Yochai says: We do not call one twisted unless he was initially straight and then became twisted. And who is this? This is a scholar who forsakes the Torah.