No one ever says, “I want to lose 30 pounds, keep it off briefly, then gain it all back, with some extra pounds for good measure.” But that’s exactly what happens to most people who lose weight. How do good intentions — and the investment of time and effort needed to lose weight in the first place — unravel?

We look for the fast track. Most traditional weight-loss plans call for adopting new food and exercise behaviors that we aren’t able to — or won’t want to — maintain long-term. It’s about doing whatever it takes to lose weight, with weight maintenance taking on a nebulous “I’ll worry about that later” quality. If we make changes we can’t sustain, we might lose weight initially, but it will come right back. It’s better to take the time to improve food quality and learn to adjust to hunger and fullness cues.

Anyone beginning to shape their behaviors with weight loss in mind would be wise to ask themselves, “Will I be happy eating this way or exercising this much for the rest of my life?”

We see a weight goal as the finish line. One danger is treating your weight goal as a finish line. Once you’ve crossed the line, the “diet” is over, a mind-set that sets the stage for regain. The truth is that the effort required to maintain new habits never ends.

A better approach is to set goals around things that you have control over, such as consistently exercising or eating vegetables each day, and let weight loss be the outcome. Identify your triggers to overeating — stress, fatigue — and build strategies to deal with them rather than relying on willpower. If you have a tendency to eat for emotional reasons, it’s critical to develop nonfood ways to comfort yourself.

We diet for the wrong reasons. Another challenge is that the initial motivators for weight loss — health concerns, an upcoming class reunion, a tropical vacation — often fade. Compliments on your changing appearance and the need to buy smaller pants can keep the motivational fires burning, but what happens when the number on the scale stops moving? Waiting for fresh motivation to strike can cause you to slip back into old habits, but being open to new ways to eat well and stay active can help keep you action-oriented. That’s important, because action is what primes the pump of motivation, not the other way around.

We have unrealistic expectations. How well our expectations match also affects motivation. People who are disappointed by how little weight they lost are more likely to regain.

• We aren’t flexible. Expect life’s inevitable curveballs. People who think in all-or-nothing terms are more likely to revert to old habits when something goes wrong, such as a storm that keeps them from getting to the health club.

Washington Post