You don’t need more willpower. You don’t need stronger willpower. You don’t even really need to “suck it up” or to “just do it”.
What you need is a better understanding of why you do what you do. Why you fail at critical moments. Why you always do what you’ve always done.
In addition, you need a better set of tools. Methods. Systems. Ways to handle the difficult times. Ways to set yourself up for success.
What you don’t need is to continue failing while you wait for that one miraculous moment when your willpower suddenly kicks in, surprises you, and saves the day.