You run up the stairs, step-by-step — and then you don't remember why you're up there. How good is your memory? Shopping lists and reminders on your phone for that one appointment. Forgetting is human, but it can sometimes be very annoying. Very few of us have a photographic memory. Otherwise, pulling those all-nighters might not have been necessary. Not everyone's collective memory is equally good either. Furbies? Gangnam Style? The fall of the Berlin Wall? What do you remember?