The modern pin tumbler lock is more or less an evolutionary step along a long line of lock designs. The basic principles of all locks are basically the same; you have some sort of hidden configuration (in this case, the lengths of each pin, or in the case of a much more primitive warded lock, the positions of the posts) which must be matched by the key for mechanical movement to be possible.
How you combine those elements takes some intuition, but if you really look around you at the world today I don't think it can be said that this sort of creativity and insight has been lost to history. We're building some pretty wild stuff these days.
http://woodgears.ca/combolock/index.html
Now you know why you had to go twice around when opening your school locker. ;-)