Of course, both of those things could easily happen tomorrow. So why aren't you selling today? Or, just as easily, Uncle Warren might stay at the top of his game for six more years, BV might grow at 10% till then, and price might happen to fall at a not-at-all-crazy 1.6 X Book at that particular juncture...... in which case you'll find yourself sitting at your computer one day in the winter of 2018, saying, "Goddammit!!! Why the hell did I get nervous and sell my entire BRK stake at $155K, when it's quoted today at $314K ??!! What the hell was I thinking??!!" It's not nearly as simple as you'd like to make it.