Why is Self-Control So Difficult Sometimes?

I was out last night with a group of friends and I was talking to a woman who is in her 50's and trying to "lose her stomach." She also had a problem controlling her urges to eat crap. We were talking and she had just finished eating 2 pieces of birthday cake. She shared with me that when she was young her mother told her "she was fat and shouldn't eat food that made her fat."
She looks back at the pictures now and she sees that she was NOT fat at all. She was at a good weight and she's carried those words of her mother into her adulthood. She finds it very difficult to control her eating now.

What I thought after we stopped talking was ......how sad for this woman---she seems to not have self-control NOW in her adult life and it probably stems from when her mother lied to her and told her she was fat.