You're confusing two different things:
-The purchase price of an item (that happens to be paid in monthly installments)
-The monthly cost of owning an item, expressed as price/lifetime (looking only at purchase price, and ignoring maintenance etc.)
For example, if you pay for a car in 96 monthly payments, that does not mean the car will last 96 months. And the car definitely won't last longer if the number of payments is increased to 192.
You can do this with all your purchases though: anytime you buy anything, don't look at the sticker price - figure out the equivalent monthly cost for the expected lifetime of the item. This can have a dramatic impact on your purchasing habits.