The real answer is almost everything. From the minute you are born, you live a different life from everyone else.
So the real answer is life. It shapes everyone differently, from the experiences to how we handle them. Even Identical twins have separate lives.
Unless you could do everything at the same time with the same person and have the same response, you are different.
That is comforting to me, because I don’t want what anyone else has. My life is mine.
On a side note, have you ever looked at a group of people together? How is it that we have that many people and not a one of them is the same? Different eyes, nose, ears, chin, size, shape, coloring, and the list goes on.
I could bring God into this conversation, but I know a lot of you have different views, so I’ll just leave it at this. Go ahead and try to find 2 people who are the same, or even close.
Delusions of Adequacy 