In 1948, the legendary baseball manager Leo Durocher declared that "nice guys finish last." Although Durocher would later deny the quote, his pithy line summarizes a popular and pessimistic take on human nature. When it comes to success, we assume that making it to the top requires ethical compromises. Perhaps we need to shout and scream like Steve Jobs, or cut legal corners like Gordon Gekko: the point is that those who win the game of life don't obey the same rules as everyone else. And maybe that's why they're winning.

Well, it turns out Durocher and all those pessimists were right: nice guys really do finish last, or at least make significantly less money. According to a new study in the Journal of Personality and Social Psychology by Beth A. Livingston of Cornell, Timothy A. Judge of Notre Dame, and Charlice Hurst of the University of Western Ontario, levels of “agreeableness” are negatively correlated with the earnings of men.

Let's begin by defining our terms. There are six facets to aggreeableness: trust, straightforwardness, compliance, altruism, modesty and tender-mindedness. Those are all nice character traits, right? Why would someone lacking those traits have a competitive edge in the workplace?

To understand why niceness might be a disadvantage, it helps to understand the essence of disagreeableness. Because being disagreeable doesn't mean you behave like Ari Gold. It doesn't mean you are a sociopath or intentionally inflict pain on others. Instead, those on the disagreeable spectrum are generally pretty decent folks, described by their peers as mostly amiable. However, these disagreeable people do consistently exhibit one special trait: They are willing to "aggressively advocate for their position during conflicts." While more agreeable people are quick to compromise for the good of the group – conflict is never fun – their disagreeable colleagues insist on holding firm. They don't mind fighting for what they want.

To tease apart the relationship between agreeableness and income, the researchers began with a data set consisting of nearly 9,000 people who entered the labor force over the last decade. The subjects were repeatedly interviewed about their career and given a battery of cognitive and personality tests. Levels of agreeableness, for instance, were measured with a standard set of questions, such as, "Do you feel that agreeable describes you as a person, where 1 means quarrelsome and 5 means agreeable?” or “How much do you feel that difficult describes you as a person, where 1 means cooperative and 5 means difficult?” These ratings were then compared to income data.

The results were bleak. The first thing the researchers discovered is that women entering the workforce earn much less than men. Even after controlling for education, marital status, hours worked per week and workforce continuity, young women still earned $4,787 less than their male colleagues, an average loss of nearly 14 percent. But the news was also dismal for aggreeable men, who earned nearly $7,000 less than their disagreeable peers. (Agreeable women weren't nearly as bad off, earning only 1,100 less.)

In a series of follow-up studies, the researchers replicated their results, showing that agreeable men earn less even after controlling for a long list of variables, including other personality traits and the possibility that nice people choose less lucrative professions. The researchers summarize their data:

Overall, across the first three studies, men who are one standard deviation below the mean on agreeableness earn an average of 18.31 percent ($9,772) more than men one standard deviation above the mean on agreeableness. Meanwhile, the “disagreeableness premium” for women was only 5.47 percent ($1,828). Thus, the income premium for disagreeableness is more than three times stronger for men than for women.

What's driving this depressing correlation? In their final study, the researchers conducted an experiment on 460 undergrads in a business management class at a large Southern university. The students were given eight hypothetical job candidates, all of whom were described as smart, insightful and conscientious. However, their levels of agreeableness were varied, so that some candidates were described as much more trusting, altruistic and humble than others. The undergrads were then asked which of these male and female candidates should be fast-tracked for management.

Once again, the results were unfortunate: Those candidates with higher levels of agreeableness were much less likely to get fast-tracked, especially if they were male. (Women were slightly less likely to get picked for promotion regardless of their personality.)

This suggests that nice guys finish last because people are subtly biased against them. Although agreeable people are less likely to get fired, and are just as likely to supervise others, they appear far less effective at negotiating pay increases, thus suggesting that the main financial benefit of disagreeableness is a willingness to stubbornly fight for what's wanted, even if it makes others uncomfortable. In addition, the researchers argue that agreeableness is particularly costly for men because it violates our gender expectations. Since we assume men will selfishly pursue their interests – please pardon the lazy generalizations – we tend to look down on those who do not, which leads to a "backlash" against unselfish and altruistic men. In other words, we expect the worst and punish the best.

But the news isn't all bad for nice guys. A new study points out that kindness is the single most salient variable that women look for when choosing a significant other. (Not surprisingly, those looking for a quick fling care most about looks.) So being agreeable won't make you rich. But it just might help you fall in love, which will make you much happier than a marginal boost in income.

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