Let's face it, on January 1st everyone is too occupied with recovering from the party the night before to be bothered with doing anything.
On January 2nd everyone is beginning to remember what happened at the said party and wondering about emigrating.
In any case, character is destiny: unless you are the sort of person who embraces violent changes of lifestyle with delight and determination, then all that going-to-the-gym, no-carb, no-moaning, being tidy, finishing A Brief History of Time stuff is quite, quite doomed. You're going to end up jogging along this year much you did last (though probably without doing any actual, you know, jogging).
Still, as you relapse, it might be possible to make a some small swerves in the right direction. If you walked to the gym then you wouldn't really have to bother with the going-in bit. Stephen Hawking's great work may be forever out of reach, but you could look up space-time continuum on Wikipedia. You could try some brown carbs instead of white ones from time to time.
And anyway, you weren't that bad to start with, were you?
Thing To Do Today: relapse. This word comes from the Latin relabī, to slip back, from labī, to slip or slide.