Most active investors have at least one 'what if' story that dogs them. Whether it involves not investing in a business partnership that profited or selling a stock prematurely that ended up skyrocketing, it is disappointing.

It is natural to grieve the one that got away, but ideally, for every missed opportunity, there is a lesson learned. Unfortunately, in these five situations, the lesson learned probably wasn't as sweet as the opportunity they whiffed on.

1. Apple Co-Founder's $50 Billion Blunder

The details: In a garage in 1976, a group of guys started a computer company that would change the world. You've probably heard of the two Steves involved: Steve Jobs and Steve Wozniak. However, there was a third founder of Apple (AAPL) who wrote the first partnership agreement, wrote the manual for the Apple I and even drew the first Apple logo. That man was Ronald Wayne.

The reason why you probably never heard of Wayne is that less than two weeks after founding Apple and receiving a 10% stake in the company, he sold his Apple stock for $800. (He reportedly got another check later for $1,500 to forfeit any claims he had against the company going forward.) Today, his stock would be worth more than $55 billion.

The lesson: Why would Wayne bail on Apple so early? He had been burned before. An earlier venture of Wayne's buying and selling slot machines fizzled and left him paying back creditors for two years. When Jobs began taking out loans to fulfill their first order, Wayne, who as a partner would be liable for any debts incurred, got skittish and sold his stake.

The bottom line is all investments have some risk. If Apple failed, Wayne may have had to work hard for a couple of years to help pay off their debts as he did before, but by bailing he missed out on untold riches as a part of one of the most successful companies ever. If you cannot handle risk, do not invest, because every investment has some risk.

As for Wayne, he seemed to be at peace with his decision, telling Bloomberg in 2011, 'If I'd stayed with them, I was going to wind up the richest man in the cemetery.'

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2. Outbid For A Piece Of YouTube

The details: As an investor in PayPal, Facebook, Zynga (ZNGA) and Groupon (GRPN), and as the co-founder of LinkedIn (LNKD), Reid Hoffman has a golden touch and a net worth that Forbes estimated to be $1.8 billion as of March 2012. It could've been even greater, however. In a New York Times interview, Hoffman says he was outbid for an estimated 30% stake investment in YouTube by venture capital firm Sequoia Capital in 2005 for $11.5 million. A year later, in late 2006, Google (GOOG) bought YouTube for $1.65 billion. His lost windfall: an estimated $495 million.

The lesson: Hoffman told the New York Times that YouTube 'built the right kind of technology' and that he wished he had pushed harder to at least get some stake in the company. So, there is the rub. When you are excellent at something and all signs point to success, determination and perseverance are essential to get the deal done.

3. A Real Lack Of Vision

The details: Tony Fadell was an engineer at Philips (PHG) when he started a side business called Fuse aimed at developing a hard disk-based music player and a Napster-like service to purchase songs. Fuse fizzled, and when Fadell pitched the idea to Philips, they balked on developing the idea. He turned to RealNetworks (RNWK), but after clashes with chief executive Rob Glaser, Fadell severed ties after six weeks and presented the idea to Apple. His idea was developed into the iPod and iPhone, two of Apple's most successful products.

The lesson: Visionaries, like anyone else, can have irritating personalities. If you've read the Steve Jobs biography, that quickly becomes clear. It is often the visionary's ruthless obsession with a product or idea that makes them successful, but difficult for management. It is better to foster a talented visionary to let them blossom rather than stifle them, which may drive them away.

4. Yahoo's Failed Courtship Of Facebook

The details: For years, Yahoo (YHOO) has lagged behind Google for search engine market share, so when they offered $1 billion to buy Facebook in 2006, it was a bold move. At the time Facebook had 1/10th the subscribers of MySpace, which had sold for $580 million a year earlier. It was a move that could have changed its fortunes, however, Mark Zuckerberg wasn't convinced he should sell.

While Facebook's board tried to convince Zuckerberg to sell, Yahoo announced disappointing earnings and their stock subsequently fell by 20%. Yahoo decided it should lower its bid by 20% as well and the deal fell through. Zuckerberg may have eventually sold with the original bid, but surely would have if Yahoo came back with a slightly higher one. Recent reports have estimated Facebook's current value at $104 billion with 800 million active users.

The lesson: Companies have to continue to innovate or they will be left behind, particularly in tech. Yahoo's revenues have declined because they haven't evolved and figured a way to make their model work in the future. If they had the fortitude to stick to their guns on the Facebook deal when the going was tough, it would likely be a much different story.

5. Beatles 'Have No Future In Show Business'

The details: Mike Smith was an executive in charge of evaluating talent for Decca Records when he traveled to Liverpool, England, to listen to an up and coming band. He was impressed. The band had unmistakable talent, so he brought them to Decca's London office for an audition on New Year's Day 1962. The band played 15 songs, went home and waited for an answer.

When they finally heard the answer, Decca's famous reply was that, 'guitar groups are on the way out' and 'the Beatles have no future in show business'.

The lesson: Don't discount something because it has been done before. The Beatles weren't the first four-piece guitar group, but they redefined genre and became the most popular band of all time.

There are hundreds of examples of people taking an idea invented by someone else and making it better. Every good idea can be perfected even if it isn't completely original. The Beatles started a cultural revolution doing just that.

The Investing Answer: Hindsight is 20/20, so it is easy to look back on these missed opportunities and shake your head. Yet, for every missed opportunity, there are hundreds of chances acted upon that turn out to be failures. Do your best to learn from these mistakes -- and others that you've seen in your own personal life -- and hope to never make one as costly as these.