Although only a single sperm enters the egg and gives rise to the embryo, many more are needed in the ejaculate, because they have to go through an obstacle course and get trained until they reach the egg: vagina, cervix, uterus, fallopian tube, and ampulla, which is the part of the tube where fertilization takes place.
Optimally, of the millions of sperm that are ejaculated, a few hundred thousand arrive at the correct Fallopian tube, and once close to the egg, they have to break the envelopes that surround it, thanks to a mini-pump that they have in their head called the acrosome, which pierces the layers around the egg.
Many spermatozoa are necessary to erode the layers of the ovum and they will not fertilize it until one arrives, which is not the fastest but the most opportune, which finds a freeway and connects with the internal membrane of the ovum and it is this one that enters inside the cell and fertilizes the ovum.
