SAN DIEGO (TheStreet) -- Whenever a bullish or bearish analyst veers from the pack, it's noteworthy. With Netflix (NFLX) - Get Report, it was noteworthy when Janney's longtime bear Tony Wible turned bullish just before the stock took off.

For that reason, it's equally noteworthy that longtime bull Scott Devitt (Morgan Stanley) turned bearish.

Too soon? That's what my colleague Jim Cramer said on CNBC's "Squawk on the Street" this morning. I think his exact word was, "premature."

Image placeholder title

And he may be right, but every call by every analyst, especially on a hot momentum stock, can't always be viewed as the moment of truth. It's not always about every tick of every trade. There's nothing wrong with trying to get ahead of the curve.

Momentum stocks simply can't be tied to fundamental concerns.

But sometimes, if a company has enough of a history, as Netflix does, it can be analyzed. That's just what Devitt did, in a well-reasoned report that focuses on subscriber saturation and the commoditization of "digital video distribution."

From his report:

"On the paid end of the spectrum, we think that Amazon Prime Instant Video, HBO GO, and Hulu Plus each offer compelling value to consumers and could gain momentum in 2014 as mass digital distribution is becoming commoditized and more content is becoming available for bidding. We continue to think that Netflix holds up well in comparison to these services, but since Netflix has amassed over 30MM domestic subscribers to date, we think it may be easier for its competitors to gain their next 5MM users than it will be for Netflix."

And therein lies an important point: Yes, as Jim says, the call may be premature. Who knows?! This isn't about being a hero. It's about pointing out what appears to be a looming risk, which is what Devitt did.

Reality: Netflix, at some point, will stop growing the way it has been. Competitors will gain a level of traction. Content costs will matter. When somebody who has loved the stock starts raising those kinds of red flags, especially with a stock that a market fueled by indiscriminate momentum behind its back, it's time to pay attention. I got Netflix wrong, so (it might and probably should be argued) I'm the last guy you should listen to. But I've also been around long enough to know that just as trees don't grow to the sky, neither will Netflix. If the Morgan Stanley analyst is right about Netflix, and the market loses steam, so will Netflix. If the market doesn't lose steam, but Netflix does -- all bets are off. But just remember: In 2011, when Netflix messed up, its stock plunged to $63 from $295. If nothing else, in a market where memories are like vapor, it should serve as a reminder of the risk.

-- Written by Herb Greenberg in San Diego

Follow @herbgreenberg

You can contact me at:

Herb Greenberg, editor of Herb Greenberg's Reality Check, is a contributor to CNBC. He does not own shares, short or trade shares in an individual corporate security.