Here's why:

* Diploid means having two sets of chromosomes.

* Somatic cells are all the cells in your body except for gametes (sperm and egg cells).

* Gametes are haploid, meaning they have only one set of chromosomes.

So, when a sperm and egg cell fuse during fertilization, they combine their single sets of chromosomes to form a diploid zygote, which then develops into a complete organism with diploid cells.