then who's fault? xp

Today I just read this book that said:
Mood is related to stressful EXTERNAL factors, rather than to hormones.
Really?
I always blame my hormones.
I always thought that it was my hormones fault.
In fact, one of my biggest ambitions is to defeat what my hormones’ wishes me to do.

But, what? It’s not my hormones fault??
Really huh?