Reply To: Chidushim on Daf Yomi

The simple reason above using the left hand and not the right because tefilin we place on the arm whereas we tie tefilin using the hand. Therefore it says that we should avoid using the middle finger of the left hand where we tie the retzios on and not the right hand because we use our hand to tie the tefilin on.

ברכות סב,ב

The Arvei Nachal Parashas Shlach Darush 1, explains it great detail the means of recognizing when something is an influence of the yetzer hara.
One, as mentioned above from the Chasan Sofer to see how much desire he has do to something. If his desire is overwhelming, he should question that maybe it is being portrayed by the yetzer hara as a mitzva when really it is an aveira. Sometimes we rationalize to explain an aveira and make it a mitzva on this the Baal Akedah says הרהורי עבירה קשה מעבירה explaining an aveira is worse than aveira because it because mutar and we will continue doing it.
Two, אין אדם רואה את נגעי עצמו a person does not recognize his own faults. So, he should imagine, how would he feel if someone else did this?
Three, a person wants to do something but he does not know if it is right or wrong. It has not been done before in his situation. David Hamelech felt that Shaul deserved death because he was out to kill him, but he was the King. David did something small to see how he will react afterwards. He cut Shaul’s edge of the garment and he felt extremely bad about it and he regret it as he describes it in Tehilim 7 as a stumble, a mistake. This becomes a test if the yetzer hara drives us to do something or the yetzer tov. We check our reaction afterwards. Most of the time we regret afterwards the wrong things we have done.