The S&P 500 market index has climbed 18% higher in 2021, but the rising tide left a few boats behind. Below, I'll show you the three worst performers among the 500 index members this year. Some of these tickers fell because there's something seriously wrong with the underlying businesses. These stocks should probably be avoided even if their bargain-bin prices may look tempting. Others may be fantastic buying opportunities today, because the market slashed their prices for no good reason.

So let's take a closer look at the bottom three performers of the S&P 500 in 2021, separating the wheat from the chaff.

A hand picks up gold nuggets from the dirt in a sifting basket.

Image source: Getty Images.

1. Viatris

Shares of healthcare company Viatris (NASDAQ:VTRS) have fallen 26% this year. The company, which was formed when pharmaceuticals developer Mylan merged with Pfizer (NYSE:PFE) division Upjohn last November, is off to a difficult start.

The company posted mixed results with strong sales but disappointing earnings in May, and then repeated that performance in August. You should note that Wall Street's expectations had been based on Viatris management's full-year expectations, which were soft enough to cause a 15% single-day price drop in February.

This stock is a bargain, any way you slice it. Viatris shares are trading at just 5.7 times free cash flow and 6.8 times forward earnings today. At the same time, analysts expect the company to post annual earnings growth of approximately 34% over the next five years.

On top of that, Viatris also offers a generous dividend yield of 3.2%. That's another direct result of the lower share prices.

Like Mylan and Upjohn before it, Viatris specializes in generic versions of off-patent drugs. That might not sound like an exciting growth market, but it doesn't take much more than a slow-and-steady growth trajectory to launch a lucrative rebound from these stagnant share prices.

2. Take-Two Interactive

Video game developer and publisher Take-Two Interactive (NASDAQ:TTWO) has taken a 29% haircut in 2021. That's a sharp reversal from the market-beating 70% return in 2020.

Of course, it's not easy to maintain the extreme gains that Take-Two posted during the intense stay-home economy of 2020. Revenues and earnings are still surging, just not fast enough to satisfy investors who had been betting on even higher growth rates.

Chart showing upward trend in Take-Two's revenue and EPS.

TTWO Revenue (TTM) data by YCharts

The biggest knock against this stock over the last year or so has been that it was far too expensive. That worry is fading away thanks to a combination of rising earnings and falling stock prices. Price-sensitive investors may want to take a fresh look at Take-Two at these lower prices, because the hit franchises of Grand Theft Auto and Red Dead Redemption are not slowing down.

3. Las Vegas Sands

Casino and resort operator Las Vegas Sands (NYSE:LVS) posted a 36% price drop over the last nine months. The company has not recovered from last year's coronavirus downturn, and Chinese regulators are adding more problems to the picture.

COVID-19 restrictions continue to weigh heavily on the flow of tourists and gamblers to Singapore, which was Las Vegas Sands' fastest-growing destination before the global health crisis. The tiny island-nation has only opened up quarantine-free air travel for passengers from Germany and Brunei so far. That trickle of international traffic plus a modest level of local guests isn't enough to sustain a successful casino operation.

Meanwhile, COVID-19 cases are on the rise in the Chinese province of Fujian, which is an important feeding ground for Las Vegas Sands' resorts in nearby Macao. Chinese regulators have clamped down on travel restrictions in the region. That's bad news for Las Vegas Sands, because Macao is the core of the company's global operations. 64% of 2019 revenues were collected in the Chinese resort destination.

Las Vegas Sands won't make a full recovery until the resort meccas of Southeast Asia have defeated their COVID-19 challenges, and there's no telling how long that might take. Moreover, the company is under the thumb of the Chinese government's regulatory powers, and I find it hard to get excited about a foreign company in that situation. This stock deserved a sharp discount in 2021.

Winning businesses will always beat bad-news bargains

With all this in mind, what have we learned? Should intelligent investors think about buying the three worst stocks of the S&P 500 this year?

I would recommend that you follow the sage advice of investing guru Warren Buffett, who famously said that "It's far better to buy a wonderful company at a fair price than a fair company at a wonderful price."

Two of these stocks strike me as winning investment ideas today, but I wouldn't touch the third one with a white poker chip -- at any price.

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.