For more than a year, the stock market has been virtually unstoppable. Following the coronavirus crash, we've been privy to the strongest bounce-back rally from a bear market bottom in history. But just because Wall Street remains optimistic on the market as a whole, it doesn't mean that every stock will participate in the rally.

For each of the following three ultra-popular stocks, the lowest price target from an analyst on Wall Street implies downside ranging from 50% to as much as 97%! The question is, are these bearish projections achievable or far too negative? Let's take a closer look.

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Moderna: Implied decline of 76%

First up is one of the absolute hottest stocks since the end of 2019, biotech stock Moderna (NASDAQ:MRNA). Taking into account Moderna's insane run over the past two weeks, shares are up almost 1,700% since the end of 2019. Yet according to the lowest price target on Wall Street of $83, Moderna has the potential to shed 76% of its value.

As you may be well aware, Moderna's popularity stems from its work in developing a coronavirus disease 2019 (COVID-19) vaccine. This two-dose treatment, known as mRNA-1273, produced a vaccine effectiveness of just over 94% in late-stage clinical trials, which was the catalyst that allowed the U.S. Food and Drug Administration to grant it emergency-use authorization (EUA). 

With Moderna aiming to have between 800 million and 1 billion doses produced this year, the company believes it'll top $19 billion in annual sales. For some context, this'll make mRNA-1273 the third best-selling drug in the world, behind only AbbVie's anti-inflammatory Humira and the Pfizer/BioNTech COVID-19 vaccine, BNT162b2. Moderna will also be wildly profitable in 2021, with Wall Street's consensus estimate calling for $24.57 in earnings per share, or nearly $9.9 billion.

However, Moderna isn't alone on the vaccine front. It's contending with Pfizer/BioNTech, the one-shot Johnson & Johnson vaccine, which has EUA in the U.S. and Europe, AstraZeneca's two-dose vaccine, and the strong likelihood that Novavax will be granted EUA for its COVID-19 vaccine, which produced roughly 90% vaccine efficacy in two large-scale studies. It's quite possible Moderna's market peaks in 2021 and tapers afterwards.

Valuation is a concern, too. While Moderna isn't pricey from a price-to-earnings perspective, most biotech stocks run into a brick wall when they hit six or seven times peak annual sales. Moderna is a bit above that level, as of this past weekend. While I'm not inclined to believe that $83 is a realistic price target in the near term, I do believe it's time to book profits on Moderna considering the uncertain competitive landscape and its lack of approved therapies beyond mRNA-1273.

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Shopify: Implied decline of 50%

Your eyes are not deceiving you -- that really says Shopify (NYSE:SHOP). Although the cloud-based e-commerce platform is a favorite among growth stock investors, one Wall Street analyst isn't a fan. The low-water analyst target of $825 would represent an implied decline in Shopify's stock of 50%.

The most logical reason for Wall Street analysts to be skeptical of Shopify's upside would be its valuation. I know, "growth stocks always trade at premiums!" However, Shopify's premium is pushing some boundaries.

Sporting a $205 billion market cap, the company is now valued at 46 times estimated sales for 2021 and 35 times projected sales for 2022. For some context here, Shopify ended 2015 through 2018 at 11 to 16 times sales and has averaged a revenue multiple of 28 over the past five years. 

To boot, even though Shopify is profitable on a recurring basis, it has a forward price-to-earnings ratio of almost 330. Again, there's some leeway given to hypergrowth stocks on the valuation front, but Shopify is certainly pushing those traditional boundaries.

On the other hand, Shopify has proved it's an absolute e-commerce beast. We were already witnessing businesses transitioning online and into the cloud long before the pandemic. However, COVID-19 pushed this trend into overdrive.

During the first quarter, 137% growth in merchant-solutions revenue ultimately pushed the gross merchandise volume (GMV) traversing its platform up 114% from the prior-year period. While triple-digit GMV growth likely isn't sustainable, Shopify seems a good bet to increase its share of e-commerce activity in the U.S. 

Shopify has landed some pretty big names as clients, too. Both Walmart and Pinterest are on board, and the company saw partner referrals up 73% at the end of March, compared to the prior-year period.

While I can support the idea that Shopify's upside may be limited in the near term, I don't believe Wall Street's most-pessimistic price target of $825 is in the cards.

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AMC Entertainment: Implied decline of 97%

On the other end of the spectrum is the popular meme stock, movie-theater chain AMC Entertainment (NYSE:AMC). Every single Wall Street analyst covering the company sees significant downside in shares of AMC, from the most optimistic analyst at B. Riley, whose price target of $16 implies 57% downside, to the most pessimistic at MKM Partners, which has a $1 price target on the company, implying a decline of up to 97%.

Unlike Shopify, which looks to have a bright future, AMC's most bearish price target may eventually become a reality. That's because none of the data surrounding AMC adds up.

Following multiple rounds of capital raises, AMC likely had in the neighborhood of $2.2 billion in cash during the second quarter. Keep in mind that, with the company losing a lot of money at the moment, this $2.2 billion will continue to dwindle throughout 2021.

The bigger issue, though, is the $5.4 billion in debt that'll need to be repaid in the coming years. Since AMC has effectively maxed out its share issuances, and its army of retail investors keeps denying CEO Adam Aron the opportunity to raise additional capital, all future debt repayments will need to be in cash. With interest expenses doubling and the company $473 million in arrears on its rent, there's pretty much no way AMC meets its debt obligations based on its current trajectory. The company's plummeting 2026 and 2027 bond prices indicate bankruptcy is a very real possibility.

The allegations of institutional/hedge fund wrongdoing from AMC's impassioned retail investors also doesn't add up. Despite these folks implying that nefarious activity is present via failure to deliver, dark pools, and short-selling, none of it has ever been substantiated. It's been my contention for weeks that social-media-driven misinformation from its retail investors has been the driving force behind this stock.

Although it's not going to go down in a straight line, AMC is very likely going to be walked back to the mid-single digits within the next six months to two years. There's also zero guarantee that it'll survive the next five years. That makes it a stock worth avoiding at all costs.

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.