Alias Clio has started a series on encounters with nice guys to show that alpha male types can be nice guys, presumably to play down what most people think -- that nice guys finish last.
There are two main uses of the word "nice" to describe a person: 1) pleasant and agreeable, and less frequently 2) courteous and dutiful. In terms of the Big Five personality traits, 1) refers to being high in Agreeableness, while 2) refers to being high in Conscientiousness. I propose the phrase "nice guy" not be used, due to confusion, and that "pleasant guy" vs. "dutiful guy" be used instead. What "everyone knows" is that pleasant guys finish last, while dutiful guys like the one in Clio's story may succeed.
Importantly, the guy in Clio's story likely scores low in Agreeableness -- no alpha scores high in this trait. You can't be tough minded, want to compete against or shove away others (however tactfully), or deal with troublemakers if you're high in Agreeableness. The guys Clio is describing are like military figures: their high Conscientiousness gives them a sense of duty and structure, while their low Agreeableness lets them enforce codes and whip rule-breakers into shape. (Those who are low in Agreeableness and low in Conscientiousness are badboy alphas.)
It's no wonder that Agreeableness shows the largest average sex difference in personality traits -- the equivalent of 1.5 to 2 inches in height. Pleasant guys therefore appear too feminine, as well as sexually unappealing, since much of a male's appeal derives from his projection of control and authority. Next time your pleasant guy friend complains about girls only wanting him as a friend, tell him to shoot up some testosterone.