Paraphrase: "Nothing common to the human condition can be alien to me". I think that understanding is the key to forgiving. I'm not using understanding in the sense of "I would have done the same thing" but instead as being able to accept that, given the processes in that person's mind, I can see how that person got to that point.

But understanding the sequences of thought in that person necessarily dictates that I/we/society must be alert and cautious with that person, and of course, that person's actions have consequences.