Cat experts agree that routine forms the basis of your cat's sense of security and comfort. Because cats are territorial, their routines will develop around your household and schedule.
From observing your pet every day, you'll have noticed that your cat has a pattern that it follows quite religiously. For example, your adult indoor cat might spend the mornings lying in a pool of sunshine in the corner of the dining room. Later, he watches you as you go about your household chores, and then his rigorous day winds down with a patient vigil by the kitchen door waiting for his children - otherwise known as your children - to come home. Your feline has developed these routines to protect his territory and frequently your pet's definition of "territory" includes his human family members.
As your cat grows older, he becomes less capable of adapting to changes in his environment. Your pet gets particular about even the smallest detail of his surroundings and will notice changes in food (brand or type), the consistency of his litter and even in your schedule or in the schedules of other family members. Abrupt or drastic changes in your cat's routine and environment can produce a great deal of stress, which can result in a variety of stress-induced behaviors - including litter box problems, aggression, self-mutilation or general despondency.
The best possible way to keep your cat stress free is to try to maintain your daily routine and to keep changes to a minimum. When changes are necessary, try introducing them to your cat gradually while leaving every other aspect of the routine in place. Limit exposure to new people and new foods, etc., on the first day and increase the exposure to newness over a seven-day period. If you have houseguests or other situations where the household is materially changed, remember to give your cat as much extra attention as you can.