Trusting someone requires two ingredients. First, one must believe the person has your best interests at heart. It's hard to trust a louse (unless of course the louse is on your side). Second, one must believe the person can do what he says—one must have confidence in his competence. And an important part of competence is self-control. Skill and aligned interests aren't much good if your buddy's a flake. A new set of findings reveals not only that people can perceive others' chronic and momentary levels of self-control, but that we use this information to judge others' trustworthiness.

The paper, published in the May issue of the Journal of Personality of Social Psychology by Francesca Righetti and Catrin Finkenauer of Vrije Universiteit Amsterdam, reported four experiments. In the first, subjects read about a student with money problems who either resisted the urge to shop at a record store or splurged on a bunch of CD's. Then they answered questions about the student's self-control and trustworthiness. The penny-pincher received higher ratings than the spender on both counts, and ratings of trustworthiness were fully dependent on ratings of self-control.

See All Stories In

Whom Can You Trust?

How to sort the liars among us from reliable folk—and build others' confidence in you.

Find a Therapist

Search for a mental health professional near you.

Find Local:

Acupuncturists

Chiropractors

Massage Therapists

Dentists

and more!

In the second experiment, people in couples rated their partners on self-control, trustworthiness, and behaviors indicative of self-control:forgiveness, reliability, and goal achievement. The most forgiving, reliable, and successful partners (as perceived by their sweethearts) were judged to have the most self-control and to be the most trustworthy. And, after controlling for other factors, the effects that perceived forgiveness and reliability had on perceived trustworthiness could be explained by their influence on perceived self-control. If you're forgiving, that means you can handle your shit, and that means I can trust you. Subjects were also more committed to partners perceived to have high self-control, because they trusted them more.

Studies 3 and 4 tested the effects of sensing that someone had temporarily depleted self-control. Subjects were less likely to trust another person when the person had just performed a difficult task for 15 minutes versus 2 minutes. (In study 4, trust was measured by investment in one's partner during an economics game.) Again, perceived trustworthiness was influenced by perceived self-control.

"I have rarely conducted research that yielded findings that were so consistent across different types of relationships (strangers and married couples), paradigms (experimental and survey studies), and measures, " Finkenauer wrote me in an email.

If you want to improve your friendships or romantic life, Finkenauer recommends working on improving your self-control—which can be done with simple exercises. "An increasing amount of research highlights the importance of having good self-control for the development and maintenance of harmonious, long-lasting relationships, " she said. Their findings extends this research by showing that your level of self-control is on constant display, and can be used against you. Look sharp!