When word hit a few weeks ago that Disney would acquire Marvel at a 30% premium, most Marvel shareholders rejoiced. Many of us here at Fool HQ did not, however, because it meant that one of the world's greatest stocks -- one that had been largely undervalued the past seven full years -- would no longer be publicly traded.

In fact, the marvelous Marvel motored to 1,300% gains since David Gardner's original recommendation in Motley Fool Stock Advisor in 2002 -- the seventh-best-performing non-penny stock in the U.S. stock market. That's all the more incredible when you consider the market returned just 2% during that time period.

Today is a great time to reflect back on Marvel's run, and identify three ways David and the team were able to achieve that 14-bagger.

1. Stay invested
If there's only one thing you remember from these lessons, let it be this: 1,300% vs. 2% only happens only if you're willing to stay invested through the inevitable ups and downs of the market. As David told his Stock Advisormembers, "Buying and holding great companies can earn you tremendous returns. Don't let small-f fools scare you out of patient ownership of great companies."

You will find naysayers every day of the yearwarning you to sell -- either to "lock in gains" because the market's overvalued, or to get out before further damage in a bear market. But if you've found an excellent company that continues to execute to your expectations, the best time to sell is almost never. Monster returns from the likes of Microsoft (Nasdaq: MSFT) and Wal-Mart (NYSE: WMT) did not come to those who locked in gains after the first 50% to 100% spike. Those two companies have gained roughly 3,000% and 10,000%, respectively, since their early days!

There's one other important advantage that comes from long-term buy-and-hold: Our seven-year run with Marvel gave us a long-standing perspective and large community following of the stock. This is a hugeasset. Continually following a company every day for seven years, along with the tremendous insights we gain from our Stock Advisormembers on the discussion boards, gave us insights that are hard to match from short-term-oriented traders. We're seeing this more and more from some of our other long-held companies as well.

2. Valuation is important, but it's not everything
This may seem controversial, but it's really not when you think about it. It's counterproductive to quibble over a couple of dollars in the share price of a great company -- dollars that turn into mere pennies in cost basis after multiple splits. Cisco (Nasdaq: CSCO), for example, closed at $24.25 its first day of trading in March 1990. Today, and a 2,900% gain later, that's a split-adjusted cost basis of a mere $0.08. Someone paying $30 back then would have a cost basis of just $0.10.

By definition, any company that beats the market by 1,300% over seven years was tremendously undervalued -- despite seeming overvalued using traditional measures. Likewise, "valuation concerns" kept plenty of investors out of Google (Nasdaq: GOOG) and Apple (Nasdaq: AAPL) in 2004. You have to be flexible, and recognize when traditional valuation measures are useless.

This is a nice segue to a related principle: Add to good companies over time. David actually recommended Marvel four timesover the seven years, with gains of 1,357%, 806%, 262%, and 70% for the four positions. The original 14-bagger was a life-changing gain; those who added to their positions along the way simply compounded the fun and profit.

3. The more obscure or unloved the company, the better
Back in 2002, Marvel was completely off Wall Street's radar, with not a single analyst covering the stock. The $170 million company was funneling most of its profits to paying off post-bankruptcy debt. Its small size made the company obscure, and it was unloved by most who did know about it.

But David noted a stable of 4,700 licensed superheroes, accompanying a rapidly improving business -- and most importantly, all this strength remained largely hidden, because of the stock's obscurity. Continued...