Night classes

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 discussion took 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!"