> (It's pretty easy to reveal this to yourself: just try to change one major habit. Or try to think of a single thought (like a red triangle or pink elephant) for more than a few moments.)
I don't have the ability to visualize at all (I have aphantasia), so I can't comment about visualizing triangles. I have and do change habits in small ways almost daily, and have made some big changes when necessary.
I think there is a misconception that free will involves immediate results with one simple thought that's more akin to magic than anything else. "I now no longer crave ice cream!", "Poof!", done. I think my aphantasia has helped me realize how much of our brains are not directly controllable. When a lot of people work through a problem consciously, I'm usually starting to do that then "fading away", coming back only later with or without a solution (sort of like highway hypnosis). Maybe everyone does this, but I don't hear it talked about that often, and people around me have found it strange when I do this around them. Must not be completely uncommon I guess because the phrase "lost in thought" is pretty common.
I think of our brains as housing more than just the conscious "me", it also involves other portions of the brain that aren't directly accessible. Thus we try to affect other areas of the brain in different ways. Sometimes a simple command works, other times we have to trick or cajole or excite another portion of us to do it for us, sometimes many many times (such as when instilling a new habit or changing an old one). If this cajoling, intimidating, engaging, or influencing isn't exerting free will, I don't know what is.
...unless the other parts of our brains are showing us unreliable information in order to get us to make the changes they want us to make, which I hope isn't true. But that's a fight for control which would imply free will anyway, I guess.