What is "Iveles Keshurah v'Lev Na'ar"?
R. Yonah: It is when evil overpowers a youth, and it is tied in his heart. Some people with bad Midos, their nature overpowers them more than others.
Malbim: Iveles is doubts about the ways of Chachmah; he argues with them. Even though in a person old in years, Iveles makes a root in his heart from which he cannot separate - "Evvil Yin'atz Musar Aviv", "Im Tichtosh Es ha'Evvil" (15:5, 27:22), in a youth, Iveles does not make a root deep in his heart. It is only tied to his heart, externally, like something tied via a thread or string. If one snaps the thread, the knot departs.
What do we learn from "Shevet Musar Yarchikenah Mimenu"?
R. Yonah: [If evil overpowers a youth,] do not despair from rebuking him. There is hope to uproot him from his nature in the days of his youth, with the staff of Musar.
Malbim: Iveles in a youth is only tied to his heart; via the staff of Musar, one can distance it from him.
