Why do we self-sabotge ?

I picked up The Mountain is You. I realize I self sabotage myself quite a bit. Started reading and the book wants me to ask myself WHY

I’ve been struggling to lose weight. Been trying to for years and whenever I get to a medium size, I shoot back up to L or XL. I can never make my way to my goal. I’m trying to understand why I do this.

Has anyone read this book? Why do you self-sabotage?