Guy at work found the perfect electric toothbrush for himself but was bemoaning the need to pick up replacement brushes periodically. Then epiphany strikes; what if he bought a bunch of them in bulk, getting a much better per item price and never have to buy any again! All he'd need to do is tally up average time before recommended replacement, figure it against average life expectancy, and voila, bag 'em all in one haul! He goes about making the calculations, arrives at a number... and suddenly gets rather somber. "That's not a very large number, is it?", he says.
To come to the length of one's mortality, as measured in toothbrush tips, on a Wednesday afternoon.