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: Shares of biopharma company Halozyme Therapeutics (Nasdaq: HALO) got their wings clipped by Mr. Market today, and they fell as much as 14% in intraday trading after a Wall Street downgrade.

So what: The trigger for the stock's drop was a downgrade from an analyst at Jefferies. The report cut the stock from buy to hold and tagged it with a $10 target price. The primary driver for the downgrade was valuation -- the analyst views the timing and upside of Halozyme's future positives as already priced into the stock, which leaves investors little potential for additional gains at the current price.

Now what: In Wall Street lingo, "hold" is often as good as "sell," since analysts have a tendency toward being bullish. Does that mean that you should hop on the bandwagon here and jam the sell button? Not so fast. While there may be some great work behind today's downgrade, it's still the view of just a single analyst. If you have Halozyme in your portfolio or on your radar, it's certainly worthwhile to take Jefferies' research into consideration, but it'd probably be more foolish than Foolish to abandon ship simply because of one non-bullish view.

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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.