What will happen if a magnet is brought near a compass?

Michale was playing a game of putting an iron ball through a maze into holes labelled as- home, jail, market and jungle. The rule was, if the iron ball falls into the market you lose 5 points, if it falls into the home you gain 50 points, if it falls into the jungle you lose 10 points and if it falls into the jail you lose 30 points. Five students played one by one and none of them put the ball into the hole-named home.

Robin got the trick. Michale had put a magnet under all the holes except the one labelled home. 

Explain Michale's plan. How are Michale and Robin different in nature?