Can Turtles Fly?

John Hussman isn't a stock picker—he's more of a macro guy—but he did comment in his April 30th Weekly Market Comment on how high sales growth declines as market share increases, and commented on Apple (AAPL). Kind of obvious but investors, particularly growth investors, often tend to ignore this, often to their peril. [as usual, bold highlights by me] Consider a very large, untapped market for some product. We can model the growth process in terms of how quickly that product is adopted by new users, whether there are any "network" effects where new buyers are attracted to the product because other people already use it, how frequently existing users replace their products, whether late-adopters come in more slowly than early-adopters because of budget constraints, how quickly the untapped market grows , and a variety of other factors. Whether you do this sort of modeling with a spreadsheet or with differential equations, you'll get essentially ...