A friend of mine once told me he knows for certain that time travel will never be possible in his lifetime. When I asked why, he said that if time travel became possible at some point in his future then he would travel back to his past with the lottery numbers so that he could become a millionaire. He was certain he would make himself rich by the time he was about 21 years of age. Since he was now about 25 years of age and he hadn't won the lottery then he knows his future self hasn't been back to help him therefore time travel will not be possible in his lifetime.
Simple
