I don't think the phrase is meant to be taken literally. I take it to mean that left on my own I chose to continue drinking alcohol despite increasing evidence I should quit. Was it my "best" thinking? Certainly not, but I also seemed unable to change course even though I saw the problem.
Ultimately, quitting alcohol is simply about applying our "best thinking" and not drinking. If it was simply a matter of kicking ourselves in the butt and doing that, then no external support would be needed - including this forum. However, many people find it helpful to have external support from other people, information, or tricks and techniques to stick to our "best thinking".