I shrug lamely, eyes dropping to the floor at Celestia's hooves, “I don’t know who I am supposed to be.” 

“You will find out in time, of this, I am sure,” I can hear the smile in her voice. I wish I had her confidence. “The mind is a very tricky trap - you’ll find that it is much better at holding onto things than you think. Sometimes, it just locks them away until we are ready.” 

The doctor had said something similar, that my brain was possibly protecting me from painful memories. Ponies are not emotionally equipped to deal with some of the more traumatic events that sometimes befall them - many cases of selective memory loss has been reported in the past - but what would cause a pony to lose their entire self?

Part of the "Friendship is Optimal" Universe