We’ve all been there. Sunday afternoon at a poolside BBQ, looking good, feeling good, body in the best shape it’s ever been, a month or so into your new workout regimen, and suddenly somebody shoves a paper plate loaded with potato salad, grilled sausages oozing fat, a pile of potato chips, whatever. Or maybe it’s the day of a big game, and your buddy is serving up six fresh pizzas along with soda. Or you’re driving home late, you’re exhausted, and you decide to just hit a Drive Through and pick up some junk food to go. Either way, everybody ultimately gets tempted to break their nutrition plan and eat junk, or skip their P90X workout and sleep in. Accept that this will happen to you, accept that you’ll be tempted, and then ask the question you’ll immediately ask as you look down at that unhealthy food: how bad is one cheat day?

Let’s be honest. The world will not end the moment you take a bite from that pizza slice. Your muscles won’t shrivel, you won’t bloat up a sudden 24 lbs, and you won’t lose all willpower and strength. If you’re in good shape, you’ll stay in good shape. If you’ve got good momentum, most likely you’ll maintain that momentum. So what’s the harm?

Think about your body as a water pump, one of those old fashioned ones with a crank you have to work up and down for awhile before water starts gushing out. Each time you exercise or eat right is one crank of the pump. In the beginning, it will take a whole ton of cranks to get that water gushing. You’ll be eating right, exercising right, and nothing, no startling results, until finally, a month or two down the road, all of a sudden your body will begin to noticeably change, and it’s like water has begun to explode from your pump. At that point, once the habit has been created, you’re set: all you have to do is work out and eat right, nothing extreme, and you can maintain your results. You can in effect ease off a little on the pump, and still keep that water flowing as long as you keep on pumping.

Clear?

So what happens if you stop pumping? You lose that pressure that draws the water up. The flow of water falters, that force of habit grows weaker. When you go back to pumping, you’ll have to pump a little harder than you were pumping before to build up that pressure again. If you stop long enough to let the water flow stop completely, you’re going to have to break your back to get back to where you were. See what I’m getting at here?

What makes people successful at exercise is force of habit. It’s not how hard you can go for two months, but for the rest of your life. It’s not just eating right for a week, or eating right until the big wedding date, or whatever. It’s eating right for life. So you need to build up that habit, and the best way is to just do it right for a long time till that habit is just a force of reflex. There’s no longer much effort involved, much thought; you just do what you do, you keep that water flowing, and you’re good.

So is it so bad to have a cheat day? No; not really. One cheat day every once in a blue moon is fine. But realize that what you’re risking isn’t gaining a few lbs or losing muscle, but rather damaging your force of habit. If you lose that rhythm, that momentum, than you’ve lost it all.