Can someone explain how?
As luck would have it, each time you insert a key, it would be the right one.
So we have 5 keys. If from 1st-4th time we inserted a key and it was right, there is no need to try for the 5th time because we already know the one that is left must work.
Don't be afraid to take a flying leap of faith.. If you risk nothing, than you gain nothing...