Email is such a funny thing. People hand you these single little messages that are no heavier than a river pebble. But it doesn't take long until you have acquired a pile of pebbles that's taller than you and heavier than you could ever hope to move, even if you wanted to do it over a few dozen trips. But for the person who took the time to hand you their pebble, it seems outrageous that you can't handle that one tiny thing. "What 'pile'? It's just a pebble!"

Merlin Mann, 43 Folders, May 30th, 2007, 3:02am.
Also quoted on pages 94-95 of: Here Comes Everybody by Clay Shirky, Penguin Books, 2008.