It's easy to forget, or maybe not ever really become aware of the fact that if you change your brain, your mind & behavior change.
Like if you use some sort of drug, or throw too much or not enough glucose in there, o r get drunk, or take a prescription Rx, or have a brain injury, or go thru therapy - these all change your *brain*.
What we think of as *will* is an aspect of executive function, & it's reeeeeeallly easy to fuck up someone's exec. function.
I mean, try not sleeping for several days, that'll do it too.