Picture this: You own a classic 15-year-old Audi Cabriolet convertible. Through upgrades and solid maintenance, it seems to improve with age—until it doesn’t. Eventually, the electronics go awry, the door handle comes off, the top won’t go down, and the transmission fails. Resale value? Close to zero. If you were your own client, you would have told yourself to sell a few years ago in order to maximize value—before the inevitable march of declension.