There’s an old saying that you’re the average of the five people you spend the most time with. Turns out that’s true. A large and growing body of behavioral science research shows that motivation (or lack thereof) is contagious. One study, “Is Poor Fitness Contagious?Evidence from Randomly Assigned Friends,” found that up to 70 percent of your fitness level may be explained by the people you train with. Other research shows that if you work on mental tasks with people who are internally driven and love what they do, you’re more likely to end up the same way. If, on the other hand, you surround yourself with people who have a negative attitude and are focused solely on winning the rat race, you set yourself up for a less fulfilling experience.