I fear you're missing mine. It's along the lines of the market remaining irrational far longer than logical investors can remain solvent. That uncle was sure the P/E was way too high, and he was right, and he ran out of money.
I agree that rebalancing in and of itself reduces risk to a degree.
Not only that, it keeps people from forecasting the market-- let alone being correct-- by deciding what the P/E is. If you pick an asset allocation and rebalance to it occasionally, you'll tend to buy low and sell high. If you're doing it with index funds then it's largely irrelevant to fret over P/Es.
You can invest as you suggest, and many do, but getting it right is a lot harder. I've spent the time doing that. I did better then than I'm doing now, but it was work and I'd rather have a life. If I can get 60-70% of my hypothetical max return with only about 20% of the effort, I'd have to be putting out max effort for love instead of for money.
When you're investing to get enough money for ER then you're quite happy to take volatilty and concentration risk. When you're ER, is there a reason to take volatility and concentration risk? How much more money do you need? More importantly, how much do you want to lose?
I'll just say it again...when the market as a whole is trading at 20+ P/Es, based on "forward earnings expectations" - with all the cracks that became obvious in the system - that reducing your equity exposure makes sense.
I hope you're not trying to tell me that investing in the stock market with a "forward" P/E of 20 is likely to produce the same returns as investing in the same market with a backward looking P/E of 10?
Perhaps. I don't know. I'd be rebalancing without worrying about the P/E.
I should point out that I wouldn't be reducing equity exposure, either-- I'd be cashing in highly-valued stocks and buying lower-valued stocks with about the same total equity allocation (>90%). Again that'd have to be an asset allocation that was diversified enough to cover a pretty broad swath of the total stock market. Having both Worldcom & Enron wouldn't exactly count as "diversification".
Your concentration on P/E10 reminds me of a poster named JWR1945.
Or, maybe phrased a different way, when would you ever consider reducing equity exposure? P/E=30? P/E=40?
P/E-100?
No, I guess not. Maybe it'll go to 200...
Don't know. (Don't care.) I'll point out that there's a high likelihood of the world's best forward P/E numbers being total crap, and we know how individual companies can manipulate their backward P/Es as well. The guys who get those forecasts right are the ones who take the time to get to know their businesses, and I'd rather do other things.
I suspect that in some markets, a high P/E stock (let's give it a name like, say, "growth") could outperform a low P/E stock (maybe we could call that "value"). I agree that value stock returns tend to produce a premium over the long term, but that's also because of the higher degree of risk that the company will go out of business. In other words a higher-returning value stock has priced in a higher degree of bankruptcy risk.
I hopefully sell high when I rebalance my portfolio. That's really the only time I sell anything in my retirement portfolio.
See, people do get it. It doesn't require any ability to figure out when the P/E is "too high" or "too low" or "just right", either.