I used to think my will and experience would set - that I would go from wanting to eat junk food to time for the gym and stay in the mindset of gym going until my workout was complete, after then, and forever more.
I now understand that my willpower is wavy - it doesn’t settle, it grows and shrinks.
Just because I feel like doing something all of a sudden, doesn’t mean that it won’t assimilate and change in the next moment. Actually, any willpower wins will always fade.
You must ride the wave up, and down.