If you are separated from your mother too early, she will not have a chance to complete your litter box training. Kittens need to stay with their mothers until they are at least eight weeks old. It is best if they can stay until they are twelve weeks old. You learn many good things from your mother, and litter box manners is one of these. No matter how well you are litter trained, if the box gets filthy you may decide to go somewhere else.
Some cats are more sensitive to filth than others.
Some cats will dig through the and the cheerfully, while others refuse the box if it is at all dirty. The humans should clean it daily for best results. Of course, the box gets dirty sooner, but there is more involved than this. When you deposit your products, you also deposit your smell. Humans can get around this problem by having more than one litter box in the house.