Yesterday is a point of reference for today. One may be wiser today because of yesterday. One may not be a person of who he is today if not for yesterday. If one doesn't know of how to look back of who he was yesterday he might have a mistaken perception of himself at the moment. If not for yesterday the present person of what one may become may not be possible. Yes it might be true that one may be wiser today but that is because of yesterday.