The causes of inequality are many and varied, and may be broadly grouped into three factors. The first is social condition or family background. In China, for example, someone born and bred in the city usually earns a higher income and enjoys better social services. The second is aptitude. The cleverer or stronger ones usually earn more and enjoy better conditions than the lesser endowed. The final one is ambition and diligence. All things being equal, someone who aims higher and works harder often earns more.