Having children is crucial to the survival of the human race. Without children, humanity would be dead in about one century. Without children, no survival is ultimately possible. Bearing and raising children is, therefore, the most important task possible. However, bearing and raising children is also the most difficult task possible.
Many barriers stand in the way of a child being born.
Potential parents must survive long enough to bear children. Biological parents must also be fertile enough to bear children. If those barriers are overcome, if the potential mother is in a fertile time of the month, and if the couple has sex during that time, then there is a chance that fertilization will occur. The instant of fertilization is the crucial instant in which everyone's live began. In the moment of fertilization, all of the genetic factors of the potential child are determined.