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: One day after issuing awful guidance and a week after Warren Buffett's big buy, shares of First Solar (Nasdaq: FSLR) fell 10% after an analyst downgrade. The stock closed off roughly 6%.

So what: Blame Robert W. Baird for the fall. The firm cut its rating on First Solar shares from "outperform" to "neutral," citing yesterday's guidance. Peer MEMC Electronic Materials (NYSE: WFR) also fell, closing down a little more than 5%.

Now what: Though yesterday's sell-off was fueled by lower prices, tighter margins, and weakening market conditions, today's action was based no new information and, as a result, was probably overdone. Do you agree? Would you buy shares of First Solar at current prices? Let us know what you think using the comments box below.

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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.