TStael: But had your parents aborted your younger sister, you would not be you, plus you would probably know anyhow as people suck in keeping certain kind of secrets.
You might have been missed if you were a wanted child by your parents, or your elder bother anyway. We do often enough regret results or non-results of our decisions, and this I would equate with missing - in an idealized form.
Had I been aborted, my parents wouldn't miss me but a hypothetical idea of what I could have been had I existed, and that's not me at all.
But it's true that we are the sum of our experiences. Without my younger sister, I would have never had a chance to play "My Little Pony" (I remember one of those could glow in the dark, or all of them, can't remember exactly) so now that that's taken care of I don't have to be part of the 'Bronie' movement.
And yes, we sometimes feel nostalgia for the hypothetical. We used to live in the US for a couple years when I was little and I sometimes wondered how things would have been had we not moved back to Switzerland but it is as you say, you would not be you without the experiences you have made.
Besides, skiing is better here anyway, that's for sure. It's also unaffordably expensive, so maybe I want to be back in the US now :D But if I was there, I wouldn't know that if I was here i wouldn't be able to afford it and I would miss the snow... do you see where I'm going with this...? Too many variables in life, you can get lost in a non escapable caleidoscopic fractal labyrinth and there's little use in that, to anyone. Unless you decide to become a philosophy professor and make a living trying to help society find a balance between practicality and ethics without sacrificing either.
In the meantime, a UFO with some aliens inside flies by: "Hey look Ghork-Ugurk, they have ethics now, ain't that cute!"
...