The phrase "to come full circle” is an idiom that refers to something — whether a person, place or thing — ending up in the same place it started. It most commonly refers to people. As an idiomatic expression, which is a figure of speech, it must be interpreted because it does not literally mean what it says. In this instance, “full circle” refers to the fact that a circle ends in the same place that it starts, because drawing or otherwise creating a circle requires a full revolution, which puts one back where the circle began. This can be transferred to the fact that people sometimes end where they started in terms of attitude, beliefs or career.
In terms of professions, a person might go through a series of jobs in various fields before deciding he actually likes a previous profession, possibly even the one in which he began. A person might begin his career as a chef, only to become disillusioned and leave the kitchen for a job as a bank teller. He then might decide he doesn’t like the bank and get a job managing an office, only to figure out that neither the bank nor the office is the place for him. If he then decides that being a chef wasn’t so bad and goes back to that career, it can be said that he came full circle.
Attitudes and beliefs are another area in which people sometimes come full circle. A person may begin life with a positive and hardworking attitude in childhood; become defiant, pessimistic, and lazy in adolescence; and then decide again to become hardworking and optimistic in early adulthood after seeing the negative effects of the adolescent behavior. That person also can be said to have come full circle. Similarly, a parent might begin trying to use reasoning and rewards to keep his children in line. After feeling that physical punishment might be more effective, he could change methods, only to realize that rewards and reasoning actually work better.
The idea of coming full circle is opposite of the idea of someone doing a 180, which refers to 180°, or half the circumference of a circle. The full circumference of a circle, which goes along with this concept, is 360°. People who have done a 180 have changed so that they are, in some way, totally opposite of how they used to be, although they may come full circle before they're done. A boss who began his job being unreasonable and unwilling to take feedback or constructive criticism from his subordinates and later becomes easy to work with and open to suggestions could be said to have done a 180.