One rule, held without exception, beats five rules held loosely. Compliance is built one binary decision at a time.
The instinct, when a man decides he's finally serious about discipline, is to overhaul everything at once. Five new rules. A complete overhaul of the morning, the evening, the diet, the schedule. It feels productive. It rarely survives the first difficult day.
The standing rule works differently. One rule. Small enough to seem almost trivial. Specific enough that there's no room to negotiate what counts as compliance. Not "eat better": a single, binary, yes-or-no action, done or not done, no partial credit.
The reason this works isn't that the rule itself matters more than the others he might have chosen. It's that holding one rule without exception builds a different kind of muscle than holding five rules loosely. Loose compliance across many fronts teaches you that negotiation is always available. Absolute compliance on one front teaches you what non-negotiable actually feels like, and that lesson transfers.
Once a man can hold one standing rule without exception, a second becomes possible. Not before. This is the part most self-directed discipline attempts skip, and it's the part that determines whether everything after it holds.