Belief Systems are based on and developed through our experiences. They change depending on what and whom we come into contact with. Even if an experience is shared, no two people perceive it identically. These differences in perception make Belief Systems unique to each person.
As your experiences mount, you form a set of facts and rules about them that you perceive as truth. Additional experiences solidify or bring them in to question. The facts and rules you continue to trust are kept and form your Belief System. You use these rules and facts to judge all of your experiences.
In addition, your Belief System drives your behavior. We act out what we believe every moment of every day, whether or not we are conscious of doing so. We attract circumstances to ourselves based on our beliefs. We can discover beliefs we are unaware of by examining our choices, predicaments, and behaviors. Awareness of what rules and facts comprise your Belief System is a great step in self-discovery.