10/26/2011 12:21 am ET | Updated Dec 26, 2011

The Key Trait Successful People Share

Which character traits do you need to have if you want to work effectively and get ahead? The answer depends, to some extent, on the kind of work you do -- but there's one trait that everyone needs to have if they want to succeed, and that's trustworthiness. Technically, it's not so much being trustworthy, but being perceived as trustworthy, that matters. You can be as honest, fair, and reliable as the day is long, but if nobody else sees you that way, it won't help you.

When your boss doesn't trust you, you don't get key assignments, promotions or the latitude to do things your own way and take risks. When your colleagues and employees don't trust you, you don't get their best effort, or all the information you need from them to make good decisions.

If you want other people to believe that you are trustworthy, you should be aware that you may be seriously undermining that belief if you appear to lack self-control. New research shows that people just won't trust you when you seem like you might have a willpower problem. If you think about it, this makes a lot of intuitive sense. We trust people because we know that when things get hard, or when it might be tempting for them to put their own interests first, they'll resist temptation and do what's right.

Studies show that when you engage in behaviors that are indicative of low self-control, your trustworthiness is diminished. In other words, all those things you know you shouldn't do -- smoking, overeating, impulsive spending, being lazy, late, disorganized, excessively emotional or having a quick temper -- may be even worse for you than you ever realized, because of the collateral damage they are doing to your reputation.

So if you want to be trusted, you're going to have to conquer these trust saboteurs. To do that, you'll need to understand how willpower really works, and how you can get your hands on some more of it.

The Secret to Earning Trust: Willpower

Your capacity for self-control is like the muscles in your body. Like biceps or triceps, willpower varies in its strength, not only from person to person, but from moment to moment. Just as well-developed biceps sometimes get tired and jelly-like after a strenuous workout, so too does your willpower "muscle."

Even everyday actions like decision-making or trying to make a good impression can sap this valuable resource. So can coping with the stresses of your career and family. When you tax it too much at once, or for too long, the well of self-control strength runs dry, no matter who you are. It is in these moments that the doughnut (or the cigarette, or your hot temper) wins.

So if you are serious about resisting your unwanted impulses, start by making peace with the fact that your willpower is limited. If you've spent all your self-control handling stresses at work, you will not have much left at the end of the day for sticking to your resolutions. Think about when you are most likely to feel drained and vulnerable, and make a plan to keep yourself out of harm's way. Decide, in advance, what you will do instead when the impulse strikes.

The good news is, willpower depletion is only temporary. Give your muscle time to bounce back, and you'll be back in fighting form. When rest is not an option, recent research shows that you can actually speed up your self-control recovery, or give it a boost when reserves are low, simply by thinking about people you know who have lot of self-control. (Thinking about my impossibly self-possessed mother does wonders for me when I'm about to fall off the no-cheesecake wagon.)

Or, you can try giving yourself a pick-me-up. I don't mean a cocktail -- I mean something that puts you in a good mood. (Again, not a cocktail -- it may be mood-enhancing, but alcohol is definitely not willpower-enhancing, nor trust-enhancing). Anything that lifts your spirits should also help restore your self-control strength when you're looking for a quick fix.

The other way in which willpower is like a muscle (and the really great news for those of us trying to rid ourselves of a trust saboteur) is that it can be made stronger over time, if you give it regular workouts. Recent studies show that daily activities such as exercising, keeping track of your finances or what you are eating -- or even just remembering to sit up straight every time you think of it -- can strengthen your capacity for self-control. For example, in one study, people who were given free gym memberships and stuck to a daily exercise program for two months not only got physically healthier, but also smoked fewer cigarettes, drank less alcohol, and ate less junk food. They were better able to control their tempers, and less likely to spend money impulsively. They didn't leave their dishes in the sink, didn't put things off until later, and missed fewer appointments. In fact, every aspect of their lives that required the use of willpower improved dramatically.

So if you want to build more willpower, start by picking an activity (or avoiding one) that fits with your life and your goals -- anything that requires you to override an impulse or desire again and again, and add this activity to your daily routine. It will be hard in the beginning, but it will get easier over time if you hang in there, because your capacity for self-control will grow. Other people will notice the change, and trust you more.

Armed with more willpower and the trust of those around you, you'll be more successful than ever before.

For ways to be more successful in your relationships, at work and everywhere else, check out my new book, "Succeed: How We Can Reach Our Goals." Or, visit my website, The Science of Success. Follow me on Twitter @hghalvorson.