Understanding that the stock market generally rises around 7% annually over the very long-term gives you a rational idea of what to expect.
Understanding this long-term return, you should start to wonder when TV pundits talk about double- and triple-digit potential returns in picking stocks.
The better strategy when stocks start looking expensive is a simple rules Graham outlines in the book.
1. No borrowing to buy stocks. This is called buying on margin and should never be done anyway. 2. No increase in the proportion of funds held in stocks. This doesn’t necessarily mean you stop investing in stocks, just that you invest in other asset classes.