Cracking the Code

In the Ukraine there was a self-service luggage room at a railway station with one luggage locker left conveniently open. You put your luggage into the locker, choose the code inside, put the coins in and close the door.
But it's not working! What do you do?
You get your bag, choose a new locker, put your luggage into the locker, choose the code inside, put the coins in and close the door.
But 90% of people choose the same code again.
The man who has been watching you only has to look at your first code and he can open your second locker!