Sell on Good News

I worked for almost 15 years at Lockheed Martin. I still have some Lockheed stock form those days. This morning Lockheed Martin announced better than expected earnings and the stock dropped 4 and half points.

I know that this is no unexpected. Stocks go up on bad news and down on good news, but that doesn’t mean it makes any sense to me. In the book I read about the Dutch stock market (Confusion de Confusiones by Joseph De La Vega) in the 17th century there is an explanation for this. I understood it at the time, but I could not explain it now. It is a very basic fact about free markets, but I still don’t get it.