I agree with the first sentence, but I'm not sure if our reasoning is the same. Here's mine: If humans were perfectly rational overall, buying a lottery ticket would never make sense. But we aren't. I think it's rational to buy a lottery ticket say, every six months, and then not check if it's a winner for the six months. Just as humans seems to enjoy the anticipation of an upcoming vacation more than the actual vacation, the human brain can get utility from the hope that ticket might be a winner, and 6 months of an (irrational, but so what?) hope far outweigh the one day of disappointment and one dollar lost when you check the ticket and it hasn't won.