There are few things more frustrating than losing a car key. Sure, one can take some comfort in the fact that one has not lost the whole car, but still, for those few hours it is tantamount to the same thing.
The inconvenience caused by the loss of such a simple object is immense, especially when far from home. Obtaining a spare key (if you are lucky enough to have it) is time consuming and frustrating, but it needs to be done. This too is easier said than done, as invariably you are not within a close proximity to the key and must therefore arrange a lift to the destination of said key, and then back to the car, all the time hoping that someone else has not found the desired item and driven off in your prize possession.
When you finally do arrive back at the car, spare key in hand, the mission surrounding it seems completely unnecessary, as with a simple turn you are back in your car and ready to go, as if nothing happened. Yet, something did happen, and it has just cost you a few hours of your life. That, however is not all, as the prudent owner is now faced with the cost and task of acquiring a new spare key. Having just proved its value, one cannot justify not owning a spare car key.