The phrase “market timing” is of paramount importance to investment professionals but is difficult for most people to grasp. No matter how many times the subject is broached, most people cannot internalize the idea.

The concept comes down to this: if the stock market from time to time is going to go crazy and plunge, why don’t I just sell stocks before that and buy them back when it is safe? Why suffer those losses and that pain, when it can be avoided?

If that were possible, I would certainly sign up. But all of the evidence and my own experience of 45 years of closely following the stock market support the conclusion that only in retrospect is it possible to predict market downturns. Sometimes an investor takes action before a crash or a bull market and the media trumpets their success. But then the investor makes a second call and a third and the inevitable failure erases that guru from the scene.

A recent example was the hedge fund investor John Paulson, whose shorting of mortgage backed securities before the 2007-9 collapse was the subject of the book “The Greatest Trade Ever.” Paulson then proceeded to give much of that money back quickly with a series of disastrous trades.

The examples are endless and the academic evidence is even greater. Few investors even come close to equaling stock market returns over an extended period of time and only a handful have surpassed the market over a period long enough to be at all meaningful.

One reason that it’s impossible to time the market is that the stock market tends to move ahead of the news. Normal logic does not apply and the people who are most logical and analytical — scientists, engineers, mathematicians — have the most difficulty with this.

Over time, average market returns are powerful — in the U.S. for the last century on average the broad U.S. stock market has nearly doubled every seven years. Trying to do better leads most people to do much worse. If you take the bad with the good, you’ll get plenty of good.