Pride is the root of most other sins when you get right down to it and it's the one I have in mos abundance. At my worst, I've actually taken pride in this. I've been in some very dark places in my life and my belief in my own superiority or uniqueness or being right no matter what is to blame for that.

Incidentally, while Pride wasn't my favorite Homunculus, Father was and Pride was easily his biggest sin. I always felt I could relate to his position and beliefs.