Thus far in 2020, the only certainty for investors is uncertainty. The coronavirus disease 2019 (COVID-19) pandemic sent equities screaming to their fastest and steepest bear market correction in history during the first quarter, only to see stocks stage their strongest quarterly rally since 1998 in the second quarter. It really hit home that trying to time buying and selling in the market is a fruitless venture.

But this record-breaking volatility has also opened the door for long-term investors, and allowed them to buy into game-changing and fast-growing businesses at a perceived discount. Remember, no matter how dire the U.S. economic outlook is at any given time, all stock market corrections and bear markets have eventually been followed by a bull market rally.

If you're among the many long-term investors looking to get rich the right way by purchasing great companies and hanging onto them for long periods of time, consider adding the following three no-brainer stocks to your portfolio right now.

A nearly-empty hourglass next to a stack of coins and a messy pile of cash.

Image source: Getty Images.

Palo Alto Networks

Though it may not be the fastest-growing industry, cybersecurity will be the safest and most recession-resistant industry capable of double-digit annual growth over the next decade. That's why Palo Alto Networks (NYSE:PANW) should be considered a no-brainer stock to buy.

The beauty of cybersecurity solutions is that they've morphed from a luxury to a necessity. No matter how well or poorly the economy is performing, or the size of a company, network and cloud protection is necessary to protect sensitive information. This provides cash flow predictability that simply can't be counted on in most other industries.

Palo Alto, in particular, is focused on securing enterprise clouds. We were already seeing a move from the static office environment to remote work and shared clouds long before COVID-19 hit. However, during and following the pandemic, the demand for remote work protection will only be heightened.

In particular, Palo Alto is angling to develop cloud-focused security tools in-house and has regularly been making bolt-on acquisitions designed to broaden its solutions portfolio, as well as appeal to more small and medium-sized businesses. Palo Alto's management team has made clear that spending aggressively now, even at the expense of the company's bottom line in the near term, is a smart move to secure long-term cloud-protection market share.

As the icing on the cake, Palo Alto Networks is also in the process of shifting its revenue generation away from physical firewall-protection products and toward subscriptions and services. Subscriptions are a higher-margin service that should lead to less revenue lumpiness. My expectation is that Palo Alto can grow by 15% to 20% annually throughout this decade.

A biotech lab researcher using a pipette to fill test tubes.

Image source: Getty Images.

Exelixis

Another no-brainer stock that has the potential to make investors rich is cancer-focused drug developer Exelixis (NASDAQ:EXEL).

Exelixis' golden ticket is Cabometyx, the company's lead drug that's been approved to treat first- and second-line renal cell carcinoma (RCC), as well as advanced hepatocellular carcinoma. Cabometyx has had little issue gobbling up market share in RCC and remains the only second-line indication to lead to a statistically significant improvement in objective response rate, progression-free survival, and overall survival. These two indications alone should put Cabometyx over $1 billion in annual revenue by as soon as 2021.

But what's exciting about Exelixis is Cabometyx's label-expansion opportunities. Earlier this year, Exelixis and Bristol Myers Squibb announced that the CheckMate-9ER late-stage trial of Cabometyx in combination with cancer immunotherapy Opdivo had reached its primary endpoint in first-line RCC. Instead of battling Opdivo, Exelixis has found a way to partner with its chief first-line RCC competitor to garner additional market share.

Additionally, Exelixis is raking in the cash on its high-margin (and pricey) cancer therapy. Cost of goods represents only between 4% and 5% of net product sales, and the company is generating boatloads of cash flow, even with research and development on pace to hit as much as $500 million in 2020. By year's end, Exelixis expects to have $1.5 billion to $1.6 billion in cash and investments, which would equate to between 21% and 22% of its current market cap. 

With so much cash on hand and its cash flow protected for years to come, Exelixis could become an acquirer or, perhaps, an acquisition target itself.

A person inserting their Cash Card into a Square point-of-sale card reader.

Image source: Square.

Square

Lastly, even though fintech stock Square (NYSE:SQ) has more than tripled from its March 2020 lows, the war on cash looks to be one of the most lucrative trends to invest in this decade.

Square is a company that start-up businesses and small merchants probably know well. It's been providing point-of-sale devices, sale analytics, and lending solutions to enterprises looking to get their businesses off the ground for years.

But what you might not know about Square is that it's becoming sort of a big deal with larger merchants, too. During the coronavirus-impacted first and second quarters, 52% of gross payment volume (GPV) was derived from larger sellers (i.e., those with at least $125,000 in annualized GPV). Since the U.S. is a consumption-driven economy, a bigger presence with larger merchants should lead to an acceleration of fee-based revenue.

As an added bonus, Square should benefit from the perception that cash is a harbinger of germs. This pandemic has really de-emphasized the use of cash and pushed consumers to use plastic or mobile payments. This plays right into the ongoing war on cash.

Then again, it's not the seller ecosystem that's likely to be Square's big-time profit driver moving forward. The company's peer-to-peer payment platform Cash App has been delivering stellar growth for the past 2.5 years. Monthly active user (MAU) count more than tripled from 7 million to 24 million between the end of 2017 and the end of 2019, with Square announcing that signups were at an all-time record in March and April of this year, leading to 30 million MAUs by June 2020. 

Cash App allows Square to make money a variety of ways, including through merchant fees, expedited transfer fees from Cash App users, and bitcoin exchange.

I wouldn't be shocked if Square's annual revenue (from all segments) grew more than tenfold this decade. It's a no-brainer stock to buy that's going to make a lot of long-term investors rich.

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.