Ignoring any complications presented by multiple conceptions, the sperm that successfully participates in the formation of the zygote combines with the ovum in what is effectively a unique individual. That sperm, no matter what a loser the child turns out to be, has won a greater lottery (odds of one in tens to hundreds of millions of sperms in a single ejaculate, when there might in fact be several ejaculates in the race) than any lotteries he is likely to participate in (never mind win) for the rest of his life. 

No, you would not be a totally different individual. You would never happen at all. Not only would you not come into existence at all if it had been another sperm that got there first, but suppose that the zygote did in fact split to produce two embryos, you plus an identical twin, then your twin and you would not be the same person at all, no matter how similar.

However, yes, certainly every sperm that does not make it, not only does represent an individual that it could hypothetically have made by combining with this ovum, but an indefinite number that it could have made with any number of other ova from either this woman this month, but any woman in any fertile period. We are the merest froth on a vast ocean of might-have-beens (or perhaps beans. A lot of pollen grains get eaten by bees too! Sperms are not the only wastefully-invested gametes in nature.)

And that is not even counting the fact that only one conceptus in several ever makes it, even ignoring birth control activities. Leave the remark: "Every sperm is precious" to the Monty Pythons of this world. Dame Nature subscribes to nothing of the kind.

But even if the sperm that did in fact participate in your conception won the race, every trivial accident of many that did happen to you after conception would mean that someone else had been born if it made even a tiny difference to the development of your brain. You would differ from what you might have been as much as you would differ from a twin.

You are the accidental product of accident after accident to an accident to an accident.

Yes?

Don't think about it if it makes you dizzy.  :-)

Jon

The mathematics are daunting. You have 23 pairs of chromosomes and at the time of sperm (or egg) formation one of each pair is picked. For a model, think of having all the spades and hearts from a deck of cards. If you pick one of each rank at random then the odds you pick the Ace of Spades rather than Hearts is ½ and the same is true for each card.So, the odds that you pick both the Ace and King of Spades is ½ x ½ or ¼.

For 23 pairs of chromosomes, that means there are 2^23 possible combinations, or 8,388,608. That might seem a daunting set of odds, but in reality it is far, far worse. Before making the pick of each chromosome, the two randomly exchange some of their information. There is no real way of quantifying this step, suffice it to say that there is virtually no possibility that exactly the same exchange will take place again. As a result every sperm contains a unique subset of your genetic information that will never be duplicated. The same has taken place in the formation of the egg, so every zygote formed by fertilization will be unique.