You feel great. Then time passes. Perhaps a family emergency comes up, or maybe a personal setback, such as an injury or an illness. Or perhaps a holiday hits and your strength is sorely tried. Your attention is diverted completely toward the issue at hand.
More time passes.
You realize that it has been several days since you paid attention to your program, done your exercise, drank your water, measured your portions. Get in touch with the person you were when you first set out. Realize that that blast-furnace push will fade to an inner glow over time. But it will not be extinguished unless you let it. Dwell on your successes.