There is a story in Abihem Shel Yisrael 'Al HaTorah about two Yeshibah students who were sitting in the Beth Midrash. They were discussing among themselves, a matter not pertaining to the topic they were studying.
The Mashgiyah noticed this and went to them. He listened to part of their conversation and then asked them, "What subject are you studying exactly?". One of them replied that they were discussing how they could best overcome their Yeser Hara' (evil inclination). The other nodded in affirmation.
The Mashgiyah pulled up a chair and sat down next to them. He said, "The Yeser Hara' has many ways to take a man away from his Torah studies and from his service to G-d. And it would appear that even on this occasion, it has managed to stop you from studying what you are supposed to be learning, so you can concentrate on how to overcome the Yeser Hara'. You must know, it doesn't bother the Yeser Hara' that you are discussing it, just as long as you are not studying".
We must all know that there is no end to the Yeser Hara's cunning in diverting us from our holy obligations. We must be on the lookout for it at all times.
(See Abihem Shel Yisrael 'Al HaTorah, Shemoth, Habrutha 'Im HaYeser Hara')
Yetzer Hara', Avihem Shel Yisrael, Harav Mordechai Eliyahu, Rabbi Mordekhai Eliyahu