Sustaining change is difficult to do with willpower alone because willpower becomes more worn out the more we use it. A better way is to decrease the willpower required by decreasing the “activation energy” (time, choices, mental and physical effort) for habits we want to adopt, and alternatively, increasing it for habits we want to avoid.
Decrease activation energy by reducing the time it takes to do something by 20 seconds, e.g., sleeping in your gym clothes.
Increase activation energy by increasing the time by 20 seconds, e.g., by putting the TV remote batteries in a cupboard.