2021 is not off to a good start for the Dow Jones Industrial Average (DJINDICES:^DJI) or the broader stock market, with the Dow down 1.7% at 1:20 p.m. EST Monday. With stimulus checks hitting Americans' bank accounts and wide availability of COVID-19 vaccines just months away, there are plenty of reasons to be optimistic. But valuations are historically high and talk of a stock market bubble could be weighing on investors' minds.

Shares of Apple (NASDAQ:AAPL) and Coca-Cola (NYSE:KO) were down big on Monday to lead the Dow lower. Apple stock sank despite a call for the tech giant to outperform other FAANG stocks this year, and Coca-Cola stock slumped after it was downgraded on valuation concerns.

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Apple could lead FAANG stocks this year

Loup Ventures expects Apple to beat out all other FAANG stocks in 2021. The stock surged around 80% last year, pushing the market capitalization of the tech giant beyond $2 trillion. It could be another big year for Apple investors if Loup's prediction hits the mark.

Loup based its outlook on a few factors. It expects increased working and learning from home to continue to drive sales of Apple's Mac computers and iPad tablets. Together those products account for around one-quarter of total revenue, and Loup expects them to grow sales by a double-digit percentage in 2021 and 2022.

Loup also expects demand for 5G smartphones to help Apple's iPhone sales in the second half of the year. This should trigger a multi-year upgrade cycle, Loup reckons. In the longer term, Loup expects Apple to launch subscription offerings that include hardware and services, and for a potential Apple Car to drastically expand the company's total addressable market.

Loup is expecting Apple to grow revenue by around 15% this year, followed by roughly 10% growth in 2022. That would be impressive given Apple's size and the maturity of the smartphone market. Whether consumers embrace 5G enough to drive significantly higher iPhone sales is an open question. What the U.S. and global economies look like coming out of the pandemic is also a wildcard for the tech giant.

While Apple stock could ultimately outperform this year, the first day of trading in 2021 has not been kind. Apple stock was down 3% by early Monday afternoon amid a broad stock market sell-off.

Analyst loses optimism for Coca-Cola

While Apple got some positive analyst commentary to start the week, beverage giant Coca-Cola wasn't so lucky. Analysts at RBC Capital Market downgraded Coca-Cola stock to "sector perform" on Monday due to valuation concerns.

Coca-Cola has had a rough go of it during the pandemic as visits to restaurants plunged. However, the stock has recovered much of the ground it lost since peaking prior to the pandemic. RBC feels that Coca-Cola's management is making good decisions, but that the company has no control over how things will evolve in the near term. RBC contends that Coca-Cola is fully valued, that upward revisions to EPS estimates are unlikely, and that the negative impacts of the pandemic will hurt the business for longer than many are expecting.

Failing restaurants and a movie theater business in turmoil may knock down Coca-Cola's out-of-home sales for quite some time. Fewer visits to stores could also sting, reducing impulse buys of Coca-Cola's products. The company has been dropping underperforming brands to refocus on its core portfolio, which could help boost profitability in a tough environment.

Shares of Coca-Cola were down about 4.6% by early Monday afternoon as the analyst downgrade made matters worse for the stock on weak day for the market. Coca-Cola lost about 1% of its value last year; it's already surpassed that decline for 2021.

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.