When you come to think of it, time itself is something that somewhat causes you to have multiple personalities.
Every few years (and then every few decades as you get older), you become a different person physically at least, if not psychologically, although legally you remain yourself.
With all the ways in which your thinking, feeling, willing, and relating have varied over different stages, which version of yourself is the real one? Which particular photo, for instance, best portrays the you that you want to be most remembered–your high school or college graduation photo, the shot of your wedding day, the picture of you carrying your first child or grandchild?
If there is not something or someone that is unchanging upon which all reality stands, we will all be strangers to ourselves, doomed with incoherence.