I used to do that too, but I can't tell you why. It would be one of those requirements that for some reason I would rebel against and put off. Then, like most things we put off, it became a bigger deal, almost like another failure looming, and me berating myself for not just doing it.
I do know that my life is happier and a part of it is I actively think good things about myself and try to stop when the critical parent kicks in, or when the thoughts start about what a mess, or loser I am, or how many mistakes I have made in life etc.