There's a little bit of madness in us all, and we manage to control it well, which is why we struggle sometimes to understand people who do too much of a normal thing to the point where it interferes with normal functioning.
The fact of the matter is however, that it does, and irrational behaviour isn't always conscious and rational thought. Those behaviours are protective, though destructive to those around them, but they've been practiced and perfected since childhood.
Everyone makes their own choices, like when we go out and get pissed knowing that we're going to suffer like fuck the next day, but it's our choice. It's potentially irrational, but we choose to suffer.
Our choices however, are based on our experiences and developmental history, and those exeperiences shape the beliefs we have about ourselves, the world around us, and other people. Sometimes those beliefs are dysfunctional, but drive our behaviour nonetheless. Lots of that becomes automatic, habitual, and subconscious.