The issue of self is a perhaps more complex than it appears. People are composite beings, made from lots of tiny animals called cells. I've read that every seven years, we are new people, as every cell in our bodies has, by this time, died and been renewed - I can't be sure if this true, as brain cells or long term information storage must persist. This aside, most of the cells in our bodies are not our own, do not contain our DNA, but are bacteria, coming along for the ride. Of course, even our cells have slightly different DNA and an individuality of their own. We also carry molecules of all sorts; fragments of plastic, dust, other creatures, and every chemical of life which we may breathe or eat or absorb.
When we use objects, these become part of us too. Mentally, our clothing is considered part of our bodies, and studies of the brain as well as psychological tests, have shown that using prostheses or objects, like a tennis player using a racket, incorporates this into what we consider 'us'. On a wider scale, our social connections also become part of us, to a greater or lesser extent (this is the essence of identity in peer groups, nationality, gender, species) as does every interaction and connection.
We are not only made from small individual entities, but are entities ourselves in a vast sea of life.
So, where do you end and not-you begin? The borders are ever shifting and uncertain. We are not the same people we were seven years ago, and not the same people as were yesterday.
Self can be seen like a wave in an ocean. We can identify a wave and consider it separate from other waves, but all waves are part of the sea. Sometimes, among a panoply of other waves, a wave can be lost and reappear later. Egotists should remain aware of the illusion of their self as separate from others or the world.