Advice about building routines has shifted over the last few decades from exhortation towards the arrangement of circumstances. The shift follows from what is and is not under deliberate control.
Motivation is the least controllable element
Wanting to do something fluctuates with sleep, mood, workload and health, none of which can be set in advance by decision.
Advice built on motivation therefore works when it is least needed and fails when it matters, which is the pattern most people recognise from their own attempts.
Guidance that concentrates on arrangement rather than resolve is not claiming that motivation is irrelevant. It is treating motivation as a variable rather than a lever.
A cue is a decision made once
Attaching an action to an existing event fixes when it happens without requiring the question to be reopened each day.
The event does the remembering. A person who has decided to practise after a specific daily routine does not have to notice that the time has come, because the routine announces it.
This is why such advice specifies the trigger concretely rather than a time of day, since a clock time competes with everything else scheduled loosely around it.
Environment carries much of the load
The effort required to begin an activity depends heavily on how much preparation stands between the intention and the first action.
Reducing that distance is straightforward and physical: the equipment is out, the space is ready, the alternative is less immediately available.
Traditional practice communities arrived at the same conclusion by different means, which is why monastic and household devotional customs specify a fixed place as well as a fixed hour.
Repetition changes what the action costs
An action performed in the same circumstances repeatedly requires progressively less deliberation, though the timescale varies widely between people and activities.
Popular writing frequently attaches a specific number of days to this process. The underlying research does not support a single figure, and the range reported is broad.
What is better established is the direction of the effect rather than its speed, and advice that promises a fixed timetable is overstating what is known.
Interruption is expected rather than fatal
Travel, illness and disruption break routines regularly and unavoidably, and a system that treats any break as a failure of character tends to end at the first one.
More useful framings plan the return in advance, naming what a reduced version of the activity looks like and treating resumption as an ordinary part of the practice rather than as starting over from nothing.
Contemplative traditions handle this the same way, with rules that specify how a missed observance is made up, which normalises the lapse instead of penalising it.