The stock market sometimes causes many people to lose sleep. An old Wall Street proverb is to “sell down to the sleeping point”—that is, only assume the risk that can make you sleep comfortably at night, without excessive worry.

The Wall Street proverb is cited in print by at least 1892. The saying is sometimes attributed to J. P. Morgan, although no early, direct print citations can be attributed to him.


Stock Market Adages
Buy to the sleeping point. [If you are troubled about making an investment but still feel the need to make it, make the smallest possible investment that leaves you feeling like you’ve ‘dealt’ with the need and can calmly sleep at night.  To feel obligated to make an “all or nothing” investment.]
(...)
Sell to the sleeping point. —if you are troubled by an investment but still desire to hang onto it, sell just enough so that you can feel that you’ve ‘dealt’ with the anxiety and can calmly sleep at night, but you’ve kept enough to feel comfortable with what you have left.

9 April 1892, Wall Street Daily News, pg. 4:
If your investments worry you so you cannot sleep, sell down to a sleeping point or close out entirely.

Google Books
The A B C of Stock Speculation
By Samuel Armstrong Nelson
New York, NY: Published by S.A. Nelson
1903
Pg. 149:
One man told another that he could not sleep on account of his position in the market; his friend judiciously and laconically replied : “Sell down to a sleeping point. ...

Google Books
Reminiscences of a Stock Operator
By Edwin Lefevre
New York, NY: George H. Doran Company
1923
Pg. 120:
“Sell down to the sleeping point,” answered the friend. As a rule a man adapts himself to conditions so quickly that he loses the perspective.

25 January 1942, Dallas (TX) Morning News, “Wall Street Ideas Worth Scrutiny,” section III, pg. 12:
If your stocks worry you, sell them to the “sleeping point.”

Google Books
The Big Board: a history of the New York stock market
By Robert Sobel
Published by Free Press
1965
Pg. 339:
“Sell to the sleeping point,” was Morgan’s reply. So it was for customers of soundly run, conservative brokerages. They may not have participated in many of the more spectacular rises, but they also avoided the sharp falls—and they were able to sleep.

9 November 1967, Dallas (TX) Morning News, “Sell to the Sleeping Point” by Robert E. SPear, section B, pg. 9:
The elder J. P. Morgan was once approached by a friend who said he couldn’t sleep because of his large stock holdings. “What shall I do?” he asked. “Sell down to the sleeping point,” replied Morgan.

Google Books
Buy the Rumor, Sell the Fact:
85 Maxims of Wall Street and What They Really Mean
By Michael Maiello
Published by McGraw-Hill Professional
2004
Pg. 13:
If Investments Are Keeping You Awake at Night, Sell Down to the Sleeping Point