A guy sticks his head into a barber shop and asks "How long before I can get a haircut?"
The barber looks around the shop and checks his appointments and says "about 2 hours," and the guy leaves.
A few days later the same guy sticks his head in the door and asks..."how long before I can get a haircut?"
Again, the barber looks around at the shop full of customers and says "about 2 hours." The guy leaves.
A week later the same guy sticks his head in the shop and asks "how long before I can get a haircut?" The barber looks around the shop and says "about an hour and a half". The guy leaves.
The barber says to his apprentice "I think that guy must be another barber thinking of setting up in this area. Follow him and see if you can work out who he is and where he goes."
A short while later the apprentice comes back. "I don't know who he is but he must be a friend of your wife. After he left here he went to your house!"