How does a person get to be a personality type?

From People Types and Tiger Stripes, written by Gordon Lawrence and published by CAPT.

C. G. Jung believed that we are born with a predisposition for one type. Environmental factors are very important, however, because they can foster type development or get in its way. One of the four mental processes (S, N, T, or F) and one attitude (E or I) are your natural bent, according to Jung, and these natural preferences make up the heart of type.

Type may not be clear in young people; that is, the dominant process may not yet be developed enough to organize and integrate the personality. The first task of a young person in type development is to have one of the processes emerge as leader in the personality. A later task is to gain balance by developing the auxiliary process. The other two processes also have to be developed, at least passably, because all four processes are needed every day of our lives. In middle life, some people begin to focus on their third and fourth processes and can become very skillful in them.