The first day: This time is going to be different. This time, you've got a diet plan you believe in, a house purged of temptations, a newly minted gym membership and sneakers so technologically advanced they practically run a 5K all by themselves. This time, you promise yourself, you will fully embrace a healthy lifestyle. So it's off to the gym for a cardio class, a quick weight circuit, some yoga and a lunch of naked lettuce!

Flash forward two weeks: You haven't been to the gym for a few days and that weekend wedding derailed your no-sugar-ever-again diet. But you'll get back on track... just as soon as you find those sneakers.

Flash forward one month: Gym? Who has time to go the gym? Walking is really a fine exercise and you certainly do enough of that. And the diet? Well, you've read some news stories that question the validity of a no-sugar diet. Besides, is life worth living if you can't eat chocolate-chip cookies? You've decided to eat what you like and just try to limit portion size.

Suddenly, it's swimsuit season and/or a significant event (reunion, party, vacation, etc.): Uh-oh. Wonder if that gym membership is still valid? Time to stock up on lettuce! And hey, what was the name of that diet that got Jennifer Aniston so skinny?