The lock and key is an essential component to life in civilization. As a human-made invention, the lock and key has no peer. Both its practical uses and using it to understand abstract concepts have aided people immensely. Although it is not known for sure who invented it, what is known is that it has gone many iterations of improvement, and probably still does so today, such as through computer or internet security.
The concept we are most familiar with in terms of the lock and key is inserting a metal piece that has been shaped to fit into a lock, thus turning the lock, and unlocking a door to allow access. This is convenience to selectively allow certain people in and out of a location. Cars, houses, computers are all just some of the many common places that use the concept of a lock and key, or its variations.
As always, with any invention there are advantages and disadvantages to such an arrangement as using a lock and key. Still, its many advantages help to provide the lock and key to occupy an important pedestal in society.