In essence, there were a lot of things Lex hadn't done perfectly, or even well. But he knew that his intentions were always good, and that he was always trying to improve. If, despite that, he messed up somehow, he'd just learn from that mistake. As long as he was alive, he could do something to make up for it.
With a mentality like that, it was difficult for Lex to get pulled into feelings of guilt and shame, especially during a situation like the one he was in. Perhaps there was more to the technique and his mask was blocking out key factors which would result in him falling victim to it.
But while the effectiveness of the technique dropped, it didn't change the fact that Lex was slowly getting crushed to death.
