Cats have an incredible sense of smell. Kittens are born deaf and blind but their sense of smell is already sharp and working. Within one day after birth, they can distinguish between their own home and another. They also lay claim to their own nipple and suckle from it exclusively. They know which one belongs to them by its unique smell.
Kittens are extremely impressionable.
If they do not experience and become accustomed to a variety of smells, they will have a difficult time adjusting to changes in adulthood. Likewise, if they associate a traumatic or painful experience with a particular scent, they will most likely react negatively every time they encounter it in adulthood. For example, some cats can never be taken to a groomer. Under normal circumstances, they are affectionate and trusting. But one whiff of the grooming room and they turn into ferocious animals that not even the owner can approach.