Fun famous mathematical story...
Three mathematicians and three physicists were meant to go together to a conference on the same train. They met next to the ticket office on the train station: the physicists, just like normal people, bought 3 tickets while the mathematicians bought only one. "Why?! — exclaimed the surprised physicists, — there will be a ticket inspector in the train!". "Don't worry, we have a method." — the mathematicians replied. All of them boarded the train: the physicists found their seats while the mathematicians all hid in the same toilet. When the ticket inspector came to that toilet and knocked, the doors opened just a bit and a hand popped out with a ticket. The inspector verified the ticket and went away. Thus the mathematicians managed to get to the conference with only one ticket.
The conference finished and the same six people met at the train station again. The physicists were inspired by the method and therefore decided to also buy only one ticket. While the mathematicians.... bought no ticket at all! The physicists were surprised: "How come? What will you show the ticket inspector?!". "Don't worry" — they said — "we've got a method.". The physicists and mathematicians all boarded the train, each group squeezing into a different toilet. One minute before departure, one of the mathematicians went to the physicists' toilet and knocked. A hand with the ticket popped out. The mathematician took the ticket and went back to his friends.
Moral of the story: "Don't use mathematical methods if you do not understand them."