Healy in S4 (Spoilers)

I finally got why Healy had a breakdown.

The first time I watched season 4, I thought he just broke down because he finally realized he just wasn't good at his job. Earlier in the season, and in season three, he was questioning whether he was helping anyone. He thought he could deal better with Soso, but she ended up overdosing after he recommended medication for her depression. Then with Lolly, he tried protecting her, maybe in some way, making up for his guilt in not protecting his mother. But Lolly ended up in psych, where he was trying to keep her from going.

I thought he was just taking his job failure extraordinarily hard.

However, on the second binge watch, I realize he snapped when he failed to *listen* to Lolly. He blamed himself for not listening to his mom when she was crying out for help, so when Lolly started having issues, he was going to redeem himself by listening to Lolly and counseling her. He assumed she was hearing voices when she confessed to the murder and tried to help her through them. But when the body was found, he snapped, realizing, again he had not listened to someone when he should have.

It wasn't guilt about failing at his job, it was guilt about failing his mother.