This chart below is very important. Stock prices have soared recently, but earnings expectations have risen even faster. As a result, the S&P's forward P/E ratio stood at 22.4 a year ago, but has now dropped to 20.51 as of last week.

The key is how long this growth momentum can last. In a recent report, Panmure Liberum noted that recent corporate earnings growth has significantly deviated from the long-term trend. Therefore, it believes the current situation is a "price bubble superimposed on an earnings bubble."

Meanwhile, a column in the Financial Times warns that "supernormal" profits won't last forever, and investors will eventually have to face reality.

However, the author also suggests that such growth momentum tends to persist longer than investors expect.