The great robber - Age

I know what you think I am going to talk about. About how I look at stairs and groan at the thought of climbing them, when I used to run blithely up in the past. (Not that you'll think that if you are young, nowadays. The idea of even the young running DOWN stairs, leave alone running UP, is passe; they groan at the thought as much as the old though, I bet, their knees do not make weird clicking