There's a pretty heartbreaking piece of data. Historically, if you bought a major index at a forward P/E ratio of 22-23 times, you basically shouldn't expect any ideal returns in the following 10 years—Annual Percentage Rate is basically on the ground, and sometimes it's even negative.

What does this indicate? It indicates that at this valuation height, the long-term odds are actually just this way. The expected value is really not good.

But here it is important to clarify a common misconception: saying that the long-term odds are poor does not equate to denying short-term market fluctuations. These are two different matters. In the short term, the market can still be volatile and reach new highs, but if your goal is to hold for five or ten years to double your investment, those who enter at this valuation range are likely to be disappointed. This is a lesson from history.