Social mobility refers to the movement of individuals or groups between social classes or economic levels. An open class society has high social mobility, while a closed class society has little mobility, such as a caste system. Modern societies aim to increase social mobility to make people happier and allow them to find work that suits them best. The rate of social mobility depends on both structural factors like the number of high-status jobs available, and individual factors like ability, education level, work habits, and luck. Both upward and downward social mobility can occur.