Hello

I wanted to ask what would cause a person to not do things that they know is helping them? For example, a wise person told me sugar really is bad for nerves, makes you agitated, irritable etc.
I took this on board but was too lazy to follow the advice. Fast forward many years, I was at one of the worst times of my life, & I thought I'd stop (well minimise) sugar for a week. Which I did, only had minimum sugar, via fruit & natural sources if at all.
I felt a peace which was indescribable for the times I was living in. But then I gave it up!!?
I just want to ask why would a person do that? Is there a paraliminal that could help with it?
I suppose it's self-sabotage or maybe even fear of change in that it's more comfortable to be in a state one is used to (iow laziness).

Any advice would be appreciated.