It's not that I haven't ever seen divers walking around on a boat with the mask on the back of their heads. It just took me the better part of 40 years for me to realize there was a good reason for it. It just sort of happens that I've been recently looking into ways to completely eliminate mask fogging and have done all the tricks including burning, Mr. Clean Eraser, toothpaste etc, but still got the occasional fogging. I've been avoiding putting on my mask until the very last moment before diving due to advice I received here and elsewhere and found it to be an inconvenience (but it definitely helped with the fogging issue), then I saw the backwards mask dude walking around and I was like.. "I get it".