We all fall off the wagon sometimes. Perhaps it is a destructive habit we are trying to quit that we resume, or a beneficial habit we are trying to solidify, but for some reason we temporarily lost our resolve, and we lose the momentum that got us to this point in time.
There are many understandable and common reasons that we fall out of a beneficial routine, or relapse on a harmful one. There is no need to judge yourself or your motivation. Learn from it, get back in the groove, and move on. Beneficial routines are hard to build, but easy to break. Bad habits, on the other hand, are hard to break, but progressively easier to avoid, yet always easy to return, if one is not vigilant.
There is no need to fret. Simply get back on the desired path, grab the reins a bit tighter this time, and use the experience as a reminder why you decided to start down this path in the first place.