The correct answer is intrinsic motivation
Intrinsic motivation is one that depends exclusively on the individual and is directly linked to their feelings, tastes, priorities, desires and other stimuli related to internal issues.
An individual can set some career goals and do everything possible to fulfill them. He may want a promotion or a job at a more interesting company, but he understands that to do this he needs to specialize more. Then he pursues a postgraduate or complementary course.