"What is thy name?" And he answered saying, "My name is Legion: for we are many." - The gospel of Mark.
You are not a singular individual. There is no true "personality" that you hold. Granted, some of the personalities are worn more often and can be considered to be like an old coat. Warm, safe and yours.
But still you change. Not just through growth, becoming a different person over time, but in seconds, taking on the guise of your social role. With your parents, you are a son. With your friends, you become a socialite. Your personality changes to suit the expectations of the situation.
Consider your mind to be a large coatrack. It holds many coats that can be worn. Some for summer, some for winter and even some for rain. All these personalities exist because of a certain need for them to exist.
In a way this means you could be anyone. If the need is there and is recognized as such by your mind. Some roles, however, will not appear, as there are still personal preferences. Most personalities share underlying traits and preferences. What we mistakenly call personality is simply the total of these underlying traits. What someone really is, discarding impulses to be in a specific way.
In other words : I prefer yellow summer coats.