In June 1942, an 11-year-old Warren Buffett bought his very first stock.
That was a hefty sum back then for any kid. Adjusted for inflation, Buffett's $114 would have had the same buying power as roughly $1,633 today.
Then again, Buffett did have a bit of a head start, considering his father was himself a stockbroker, so young Warren was already somewhat familiar with the idea of buying and selling small pieces of businesses through the stock market.
But that didn't make him feel any better when the price of Cities Service Preferred quickly plunged 29% to $27 per share later that month.
Even still, that drop was largely thanks to a broader market decline that year, and nothing in particular had happened to negatively change Buffett's investing thesis for the company. As a result, when the stock recovered shortly thereafter, Buffett sold at $40 per share to net a tidy 5.3% gain on his investment.
Not too shabby, right?
Here's the kicker
Shortly after he sold, however, the stock proceeded to rise to more than $200 per share.
In the end, had Buffett simply stuck to his guns and trusted his original decision, he would have more than quintupled his $114 investment to more than $600.
Or, if you prefer the illustration in today's dollars, Buffett would have quickly turned his $1,633 into a whopping $8,595.
Now most folks would probably cut the young investor some slack for this rookie mistake. After all, he was just a kid, right?
There's a name for that ...
The thing is, I'm sure I wouldn't be going out on a limb to say thousands upon thousands of adult investors make this same mistake every day.
In fact, in the world of behavioral finance, they call it the "disposition effect" -- a term to describe the tendency of investors not only to hold on to stocks that have dropped in value, but also to sell their winners too soon.
And while Buffett was right not to panic and held on to a stock for which the underlying fundamentals hadn't changed, his itchy trigger finger to sell obviously got the better of him when that stock edged into positive territory.
In the end, though, it's safe to say this lesson paid huge dividends down the road, as Buffett was able to use it as a starting point to hone his incredible ability to focus not just on the price of his equities at any given moment, but also on the actual value of the businesses behind the stocks he buys.
In fact, after the S&P 500 dropped more than 50% from the beginning of 2008 through early 2009, Buffett was the one reassuring investors everything would be OK when he released that's year's letter to Berkshire Hathaway shareholders on Feb. 28, 2009:
The market value of the bonds and stocks that we continue to hold suffered a significant decline along with the general market. This does not bother Charlie [Munger] and me. Indeed, we enjoy such price declines if we have funds available to increase our positions. Long ago, Ben Graham taught me that "Price is what you pay; value is what you get." Whether we're talking about socks or stocks, I like buying quality merchandise when it is marked down.
Those of you keeping track know the S&P 500 has more than doubled since then and currently sits near all-time highs.
Better yet, truly Foolish investors know all too well there were a significant number of beaten-down stocks around that time that have absolutely trounced the broader market's perfectly respectable return over the same period.
But in the end, those gains were reserved only for those who had managed to learn the lesson Warren Buffett first encountered as a child.
Fool contributor Steve Symington has no position in any stocks mentioned. The Motley Fool recommends and owns shares of Berkshire Hathaway. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.