Warren Buffett: Ideal purchase 

“Incidentally, the ideal purchase is something you like already when it’s selling at a price that makes you want to go out and buy more. And we probably should have done more of that in the past…. That’s one of the beauties of marketable securities. When you’re in a wonderful business, you do get a chance periodically to double up on it or something of that sort. Were the stock market to sell a lot cheaper than it is now, we’d probably buy more of the businesses we already own. They’d certainly be the first ones we’d think about buying because they’re the ones we like best.” 

—Warren Buffett (1998 Berkshire Hathaway Annual Meeting, via Outstanding Investor Digest).