Let us imagine a house. The teeth would be the columns or pillars that support the roof. If some of these columns were to be removed, the rest of them would have to support more of the weight of the structure. These remaining columns would be overloaded, and this could lead to the whole structure collapsing.
The same thing happens in the mouth when teeth are lost. The remaining teeth have to endure all the forces of mastication, suffering an important overload that could injure them and their bone support, and with time they could be lost too.