Advances in salary may become limited. By the time many people reach the middle of their careers, they are at the top of the salary scale. Top management personnel in the aerospace industry lost their jobs in the 1970's when their industry had a major recession. In industries governed by union contracts, all the low seniority employees may be laid off during a recession when there is not enough work. Companies may relocate and require employees to make job transfers.
Mandatory retirement is also something to consider.
Self-employment has many advantages. The possibility of making money is an overwhelming reason that people start their own business. There is a chance to make a profit in addition to a reasonable salary. Once the business has been successfully established, there may be financial security. In fact, statistics show that the lifetime earnings of most employees are less than the lifetime earnings of most successful entrepreneurs.