Change is not always about the brute force of the human will. If it were, dieting would be a much simpler process. Want to lose weight? Eat less, exercise more. End of story. If it doesn’t work, it must be because you didn’t really want to lose the weight, or weren’t willing to do the work required.
But it’s not that simple. It never is.
Major changes have three essential components: thoughts, feelings, and behaviors. Any significant lifestyle change is going to affect each area in complex ways. Each must be examined as you move closer to the change itself. If success still alludes you after repeated attempts, one of the three components is primarily to blame. Your mission, should you chose to accept it, is to figure out which one.
Telling yourself that you didn’t have the willpower is neither true nor helpful. So don’t do it.