Sustaining a behaviour through resolve alone tends to work for a period and then stop. Routines outperform it not because they require more discipline but because they remove the point at which discipline is needed.
Deciding repeatedly is the expensive part
A behaviour maintained by intention has to be decided on each time it comes up, and each decision is an opportunity for competing demands to win.
The decision is also made under whatever conditions happen to prevail — tired, late, distracted — which are exactly the conditions in which resolve is least available.
A routine settles the question in advance, so the behaviour is triggered by the situation rather than reconsidered on every occasion.
Cues do the work that resolve was doing
Behaviour that consistently follows a particular time, place or preceding action becomes associated with that context and is prompted by it.
The prompt arrives without effort, which means the behaviour starts before the internal negotiation about whether to do it has a chance to open.
This is why the same behaviour can feel effortful in one setting and automatic in another, with no change in the person's motivation.
Motivation is a poor foundation because it fluctuates
Enthusiasm at the start of something is genuine and reliably declines, which is a normal feature of novelty rather than a personal failing.
Anything requiring high motivation to happen will therefore stop when motivation returns to its ordinary level, which it always does.
Designing for the low-motivation state rather than the high one is the practical implication, and it usually means making the behaviour smaller.
Friction determines what survives a bad week
Every additional step between the intention and the action is a place where the sequence can break, and steps that are trivial when motivated become decisive when not.
Reducing friction — preparation done in advance, equipment already accessible, no scheduling required — has more effect than increasing commitment.
The reverse also holds: adding steps in front of an unwanted behaviour reduces it more reliably than resolving to stop.
Interruptions are the real test
Illness, travel and busy periods break routines, and the loss of the cue matters more than the missed occasions themselves.
Restarting deliberately, at a smaller scale than before, restores the association faster than waiting for conditions to return to what they were.
Treating a break as an expected event with a planned response, rather than as evidence about character, is what separates practices that resume from those that end.