Neurons in the brain, sometimes called mirror neurons (although whether or not they are a new and distinct class of neurons is still under debate) tend to fire when they observe the actions of others. When you observe someone else’s behaviors, these mirror neurons fire as if you were actually doing what you are watching. It’s as if whatever actions are being observed by the mirror neurons is happening to their host brain. Mirror neurons make no judgments regarding good-bad behaviors, they simply are quick to mimic what you observe. Within three years you will likely pick up the behaviors of those with whom you hang out. Choose with care who you hang out with during your discretionary time. Close contact between people spreads habits, especially smoking cessation, obesity, and happiness. Now it turns out that cognitive vulnerability, which can lead to symptoms of depression, may be catching as well. Choose friends who choose to be happy and who have or are developing a positive thinking style.