Yesterday, James O’Shaughnessy posted a long and intriguing tweetstorm about investor ignorance. O'Shaughnessy is the chairman and founder of O'Shaughnessy Asset Management LLC, and the author of the classic investing book “What Works on Wall Street.” The thread is worth reading from start to finish.

This post, as regular readers know, was about one of my favorite subjects. To be more precise, it was about our own lack of understanding of own lack of understanding. From the original work by Daniel Kahneman and Amor Tversky, as laid out in their famous 1974 paper "Judgment under Uncertainty," to the Dunning-Kruger concept of metacognition -- the specific skill needed to recognize one’s own skill set -- this foible continues to be of great importance to investors.

O’Shaughnessy starts his discussion on a note of humility, writing there are “some things I think I know and some things I know I don’t know.” That simple observation places him ahead of oh, say, 80 percent of all investors. This is not how way too many investors think.

The first step is recognizing what it is you know you don’t know. For O’Shaughnessy, this begins with the simple question, one that is asked every day by financial journalists in print and especially on television, discussed among retail stock brokers, and debated by fund managers: How will the market perform this year or next? This is often paired with a related question: Will stocks be higher or lower in five or 10 years? O'Shaughnessy notes what the probabilities are -- stocks do tend to rise over time -- but then says he can't say with any degree of certainty if stocks will indeed be higher a decade from now.

This acknowledgement alone bumps him up to the 90th percentile of wisdom among investors.

Most people don't even try to envision what they don't know. This brings to mind, of course, that felicitous phrase coined by former U.S. Defense Secretary Donald Rumsfeld, "unknown unknowns." The human brain, marvelous as it may be, has a blind spot for these. But, truth be told, the universe of what we don't know is beyond our grasp, even though we tend to fool ourselves into thinking we know more than we do.

Read the full article at Bloomberg.