Ok, I'll bite. Why must my cat constantly open my T-Shirt drawer and dig through said T-Shirts until precisely half of the contents of the drawer are on the floor?
Why did one of our previous cats chase his tail like it was some kind of alien object? Complete with "stalking" and "catching" his tail and then proceeding to "consume" it? (He wasn't the brightest bulb in the box) I should mention that numerous "mice" "shoelaces" and other entertainment devices were available and ignored in prefernce to the Evil Tail of Doom (tm).
A few reasons actualy, cats are not only curious and investigative, they need to keep busy due to an uncontroled urge to act its part in the wild. Just because its named a domesticated cat, doesnt means its had its wild bred out of it like a domesticated dog. They will prowl your house searching like it would in the wild, if it where looking for food, but without having any time in the wild it doesnt know what its actualy searching for. Plus another reason cats make a mess and tend to break and knock over items, is they know it will get your attention, something they really crave. Once a cat begins to rub up against you its claimed you and will expect to be pampered and have its needs met.
The tail, this is another issue of keeping a cat indoors, while it can sometimes be fleas or certain skin disorders causing it to attack its tail, it can also be a mental disorder from being eather neglected or having difficultys adjusting to the confines of living indoors. Allowing a cat to have time to itself to prowl and roam outdoors can illliminate this, plus more affection from thier owners really helps too, they need that attention. A cat will tell you when it needs this, by rubbing up against you, meowing, or getting in the way, its attention getters will become more extreme until you give it what it wants.