Peter Thiel: People take it for granted that their retirement funds can earn 8.5 percent a year. That’s what their financial planners tell them. And sure, you look back over the past 100 years, the stock market has generally gone up 6 to 8 percent a year. But in a larger historical perspective, that kind of growth is exceptional. If you had done the equivalent of investing in the stock market from, say, 1000 to 1100 AD, you would not have made 8 percent a year. During the fall of the Roman Empire, you’d have been lucky to get zero. We’ve been living in a unique period of accelerating technological progress. We’ve gone from horses to cars to planes to rockets to computers to the Internet in a very short time. It’s not automatic that that continues.