I have strong willpower.

People with famously strong willpower are usually the ones who have arranged to need the least of it. No biscuits in the house. The bank transfer that leaves on payday before the money can be thought about. A route home that does not pass the shop.

From outside that looks like discipline. From inside it is closer to admin, performed once, on a calm afternoon, on behalf of a future self who will be tired and outnumbered.

Every decision made in advance is one you do not have to win at half past ten at night.