It's one thing to think that you might be missing out on a good real estate investment, but it is another when you actually know that you did.
Still, you don't have a crystal ball and couldn't know for sure at the time that that property would be so profitable. Buying and selling real estate is risky and no sale or transaction is guaranteed until the ink is dry on the closing papers.
Fortunately, there are still many opportunities to turn a profit on in the current market. However, the more profitable strategy may be to buy and hold, verses flipping...and If you can do that you might be able to make more money than the $40,000.00 that got away.