How do you pick who to be?

How do you decide who to be in terms of personality, appearance, likes and dislikes, style, gender, sexuality etc? If you feel drawn to different identities at different points in time, how do you decide which one to commit to and make your permanent identity? For example if sometimes I want to transition to male, and sometimes I want to be female, how do I decide which one? Or if my morals and beliefs change from day to day how do I pick one to make permanent when they equally feel real and true at the time? How does anybody decide and commit to an identity?