“Reward is often correlated with risk, where risk can either be quantified as volatility or qualified as uncertainty (lack of knowledge). This means that the higher the return rate, the higher the risk of loss of capital. Another principle, however, says that risk is more related to skill and knowledge. Both of these statements are true, but for different reasons. If you think about a fast race car, it’s a more risky vehicle to drive, but if you know how to drive it, the risk goes down. There are two conclusions from this. First, having a margin of safety in terms of principal is a good idea. In other words, having a low withdrawal rate is safer than a high withdrawal rate, because the required rate of return is lower. A larger fund thus allows for more safety. Second, invest in what you understand rather than what people tell you. This is the main reason I’m not telling you what to invest in. If you don’t know anything about investing, make it a point to learn!”

“Monte Carlo simulations suggest that a withdrawal rate of 4% is good for 30 years of inflation-adjusted expenses and that a withdrawal rate of 3% is good for 60 years or more. A withdrawal rate of 2% will last forever–that is, if history repeats itself.”

“In summary, the organic growth of any sector seems to concentrate around 3% real growth. This is the number I would use as a safe withdrawal rate. It’s difficult to judge whether this number will be representative of the next 50-100 years.”

作者在最后几章里提了一些基础的财务相关的计算和原则。这里聊了一下safe withdraw rate (SWR), 作者觉得3%对于他自己来说会是非常舒服的百分比：假设退休时有100w，那每月消费就是100w x 3%/12，然后每月按CPI调整。这和我最近看的一个博客Big ERN里面的分析基本一致，当然博客里写了更多仔细的分析，并且用了historical simulation并没有用Monte Carlo，原因博客也讲了。虽然美国的情况并不能代表全世界，过去也不能预测未来，但个人觉得如果一定要我猜一个数的话，60年退休期，最终资产为0，最安全的取出率应该在3-3.5%之间。