When asked what was the dumbest stock Warren Buffett ever bought, do you know what he said? Surprisingly, he said his own company, Berkshire Hathway!
For those who want a quick synopsis, he was infuriated with the then-CEO, and bought a majority share of the company to get him fired. That's how he also became the head of Berkshire Hathway.
However, had he thought it through more clearly, and started out with the insurance company that he had wanted in the first place (Geico?), rather than a down-trodden textile company (just to get one man fired), then he say his financial empire would be worth $200 billion today!
In a nutshell, it's best to keep emotions out of investing and trading. Let the numbers do the talking. That being said though, I have to give old man Buffett respect for being able to point out his own mistakes. Even the best are only human.
On a separate but related note, here's a funny comic I came across. Buy! Buy! Sell! Sell!