Back when I was at university studying Electrical Engineering we had a Professor who was very sociable, every weekend he would invite two or three of his students to tea at his home and his wife would bake a cake.
Well, it came to my turn. I sat there drinking his tea and eating the cake, then drinking more tea. Eventually a toilet break was needed. As I stood there I noticed that there were two rolls of toilet paper, one roll of soft and another one of the hard stuff like tracing paper that you used to see in public toilets.
The two rolls were a mystery that bugged me all afternoon and eventually my curiosity got the better of me so I asked the lady of the house about the arrangements. "Oh, that's easy" she replied, "The soft paper is for normal use and the hard paper is for William to write on if he gets a good idea whilst sitting there".