Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Molycorp (NYSE: MCP), probably the most famous of the rare-earth yo-yo stocks, is spinning its way back down to earth today -- just 24 hours after Dahlman Rose gave it a yank and pulled the price up 10%.

So what: Yesterday, Dahlman gave its blessing to Molycorp, Rare Element Resources (NYSE: REE), and Avalon Rare Metals (NYSE: AVL), sending the shares of all three companies flying. But so what? These analysts change their minds on stocks faster than a 10-year-old yo-yo grand master can show you how to "walk the dog." And as you can see in today's price movement, enthusiasm over an analyst upgrade can fade even faster. Buying a stock on an analyst's say-so, without knowing why you're buying, is a fool's errand (with a lower-case "f").

Now what: If you want to trade Molycorp -- more power to you. But for the love of Pete, please make sure you can name a reason for your trades. Buy it because rare-earth metals prices are surging. Or because you think the company's 22 forward P/E ratio is cheap. Or sell it because you think the clock's ticking on China's throttlehold over the rare-earth market. Or because you think the company's got more promises than potential. Just don't do either one because some analyst tells you to.

Starved for reading material? Add Molycorp to your watchlist, and I guarantee you'll see more than enough articles to keep you busy.

Fool contributor Rich Smith does not own shares of, nor is he short, any company named above.  The Motley Fool has a disclosure policy. Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.