Funny - I hate carrying an umbrella - and usually dont; yesterday I opted to carry one to SF, and forgot it on BART. Luckily I was at the last stop in Dublin, and when the train turned around a few min later, I got it back, and...I was kind of disappointed :) I thought "There, that'll teach me to carry an umbrella!" but I (ruefully) got it back. Funny thing, the train operator told me, "If you ever need an umbrella ask us (BART); we have, like, 300 of them downstairs!" Heh heh - just an anecdote - maybe it's also people feeling guilty for taking something they know they should/could carry/afford to buy?