It must be something to do with the fact it is the one time of the day when our mind is free to wander wherever it may and our subconscious finally gets the opportunity to wave its hand in the air and catch our attention.
The only problem for me is that I've found my mind wanders so far that by the time I am out, dressed and in front of a notepad and pen again I've invented so many things and solved so many global crises that I've totally forgotten that first brilliant idea for a novel that was surely going to be the next Harry Potter if only I could remember what it was about.
Therefore, I was rather excited to find that someone has actually created a solution. AquaNotes are waterproof notebooks that can be mounted on the wall of the shower. You can write down all your brilliant ideas as they come through your mind and then rip off the sheet and take it out of the shower with you. Why didn't I think of that? Now where's my shower cap?