I doubt that more than a tiny percentage of people who claim to have caught "the flu" actually had influenza. For years I thought I got the flu each winter....until I REALLY got the flu (H1N1) two years ago. There is a world of difference. I lost 12-pounds in two weeks. My entire family got it; my son's was compounded by pneumonia and we were concerned about whether he would make it. As Velo-G said, you don't recover from it in a few days or even a week....you can feel the lingering impact for a month or more. So, I get the shot to lower the odds of ruining a big chunk of training time.