"The economy has changed. The way investors think about valuation has to change, too. This is a case that’s harder to make when the valuation differential between tech and value stocks is so stark. A correction at some stage would not be a great surprise. The appeal of old-style value investing is that it is tethered to something concrete. In contrast, forward-looking valuations are by their nature more speculative. Bubbles are perhaps unavoidable; some people will extrapolate too far."