Career decision making and identity development are interconnected in modern-day capitalist economies and societies. From an early age, the education system puts people on a path towards career goals as an adult.
From a psychological point of view, a person's identity--composed of a fixed or ever-changing personality, ideologies, and perspective on the self and the world--influences their chosen career(s). Personal experiences are also factors in choosing one's vocation.
For example, a child who experienced the loss of a parent due to cancer might be inspired to enter the medical profession, or a person who grew up in a military family might be influenced to follow the tradition.
Likewise, one's chosen vocation could influence their personal identity. For example, a person who has chosen a religious vocation (e.g. Catholic priest, Buddhist monk, et al.) will more than likely follow a lifestyle that reflects their vocational ethos and rules.