Psychology has neatly classified personality into a well-known schema called "the Big Five." These five primary personality characteristics include many facets, all of which have been studied extensively. One of these, Conscientiousness, has been found to be the most predictive of overall success. Conscientious people are reliable, persistent, and plan ahead.
Your personality not only helps determine how successful you will be, but also leads to identifying who you want to be around. In a five-year study of hundreds of people, Thomas Corley found one key differentiator between millionaires and others: Wealthy people--especially self-made--avoided pessimistic people. Self-made millionaires in particular, he found, shared how they were optimists and tried to avoid people with a pessimistic personality.
In fact, he found that nearly nine out of 10 millionaires sought to be around people who shared a positive outlook and focused on success. This is critically important when you consider that personality and habits are contagious. Just as a negative person can bring down the mood in a room, an optimistic person can lift it. While a "devil's advocate" view can be useful in the short-term, success over time requires a positive outlook.
The lesson is simple: A positive outlook and associations will take you further than a cynical view and crowd.