Chatting to many of my challengers over the last few days, and it seems motivation is sometimes letting you down....
Feeling motivated is an emotional state, and like all emotional states, it rises and falls, kind of like the tide; so if you're relying on motivation to keep you on track you will sooner or later (usually sooner) feel a lack of motivation, and unless you have another way of staying on track, then you're going to fall off the wagon (and probably start beating yourself up over it).
So you might then try to rely on willpower... but this takes mental energy, and the more decisions or choices you are faced with over the course of your day, the more drained you are of mental energy.
So where does that leave us?