Key Control - Securing the key to your possessions

The title may seems to be confusing, but, definitely it is right for what it is all about. Keys are important companion to our daily living and there would be at least one key in the pocket of every individual, it could either be of a car, property, bank locker or anything at work. But, what concerns most about it is, how secure is a person with a key that could be stolen anytime or even misplaced and forgotten?