Have you ever made a conscious effort to create a new habit?  This could be embarking on an exercise routine, changing how your fuel yourself with food/ drink, waking up early, or anything else that is new and will help you achieve a goal you want to reach and maintain.  If the answer is yes, than you know that at the start it is fairly easy to begin strong, feel extremely committed and on course, but that at some point the initial high and good feelings that come with a renewed effort to take better care of yourself wane a bit.