Night Shift

During work Mike and John are chatting, Mike: "I've been taking night courses for five months now, and I have an exam next week." John: "Oh!" Mike: "For example, do you know who Graham Bell is?" John: "No." Mike: "He is the inventor of the phone in 1876. If you take night courses you would know this." The next day the same discussiontook place: Mike: "Do you know who Alexander Dumas is?" John: "No." Mike: "He is the author of "The 3 Musketeers". If you took night courses you would know this." The next day, once again: Mike: "And do you know who Jean Jacques Rousseau is?" John: "No." Mike: "He's the author of "Confessions", if you took night courses you would know this." Now this time John got irritated and said, "And do you know who Steven Turner is?" Mike: "No." John: "He is the guy sleeping with your wife! If you stopped night duties you would know this!"