Motley Fool Co-Founder and Chief Rule Breaker David Gardner says great investors are never afraid to buy great companies trading at highs, and they never shy away from adding to their winners.

So that stock you've been watching is suddenly up 20%, huh? Think you missed your chance to get in while the getting was good?

How about the stock that has doubled since you bought it a few years ago? It doesn't make sense to pick up more shares now, does it?

What about the company whose stock is trading at more than $200 per share now? That's too much money, right?

Not so fast.

As a case in point, in June, David re-recommended that members of the Motley Fool Stock Advisor service purchase shares of online travel company (Nasdaq: PCLN) -- even though it was trading at far more than $300, and had already netted an eight-bagger for investors who got in with his first 2002 recommendation.

Was David crazy? Not at all. In his thinking, Priceline's fundamentals were still strong, management was as engaged as ever, and the company was turning in extraordinary, industry-leading growth rates. So in he went again. The result? Priceline's stock has doubled in the five months since David's re-recommendation, and has now achieved 16-bagger status for stout-hearted Stock Advisor members.

The lesson? Don't be afraid to add to your winners. Sometimes, throwing good money after good makes all the sense in the world. Watch the video here:

Fool co-founder David Gardner owns shares of, which, as mentioned, is a Motley Fool Stock Advisor selection. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.