Given how volatile the stock market has been in 2020, you might assume that investing is pretty complicated. After all, we witnessed the S&P 500 lose a third of its value in less than five weeks, then recoup all of its losses (and then some) in the subsequent five months.

But the fact is, investing isn't difficult. The secret to big gains is simply buying into great companies that offer sustainable competitive advantages and (here's the key) holding them for long periods of time. Since every single correction in history has eventually been wiped out by a bull market rally, any notable downside in the market represents an opportunity to buy, assuming you have a long investing horizon.

Furthermore, you don't need to be Warren Buffett or a Rockefeller to make money in the stock market. If you have $10,000 to put to work, that's more than enough capital to build wealth over the long run. With time as your greatest ally, here are four stocks you can invest $10,000 in right now that shouldn't have any trouble doubling your money.

An hourglass next to a stack of coins and cash.

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Teladoc Health

Don't let Wall Street tell you there's no such thing as easy money. If you've got the time, telemedicine giant Teladoc Health (NYSE:TDOC) will make you the money.

As you might imagine, the coronavirus disease 2019 (COVID) pandemic has been a monumental positive for the company. Total visits more than tripled during the second quarter, with total paid U.S. membership rising 92% and visit-fee only access jumping 125% from the prior-year period. But this isn't just a pandemic play. We were already witnessing a discernible shift toward increased telemedicine use well before COVID-19. That's because it's more convenient for the patient, a timesaver for physicians, and cheaper for health insurers. 

Furthermore, Teladoc Health is in the process of acquiring applied health signals company Livongo Health (NASDAQ:LVGO) in a cash-and-stock deal. Livongo's solutions cater to people with chronic illnesses and lean on artificial intelligence to send tips and reminders to these folks to induce long-lasting behavioral changes. Livongo has consistently doubled the number of its members with diabetes. It also reported three consecutive quarterly profits. Once these two companies combine, the result will be one of the fastest-growing precision medicine businesses on the planet.

A vial of liquid lying atop a bed of dried cannabis flowers.

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Cresco Labs

Marijuana stocks have been a crowded trade for the past couple of years, and recent growing pains have shown that there aren't many high-quality companies. Yet, cannabis is projected to be one of the fastest-growing industries in North America this decade, which bodes extremely well for U.S. multistate operator Cresco Labs (OTC:CRLBF).

One reason to absolutely love Cresco is the company's acquisition of Origin House. Investors weren't too thrilled about the deal when it closed in January, but it's going to serve an important purpose. You see, Origin House was one of only a select few companies to hold a cannabis distribution license in California, the leading marijuana market in the world by annual sales. This means Cresco is now able to get its products into more than 575 dispensaries in the Golden State.

Beyond what should be an exceptionally successful wholesale model, Cresco Labs also has a burgeoning retail presence in Illinois. The Land of Lincoln opened its doors to adult-use weed sales on Jan. 1, 2020, with nine of Cresco's 19 operational dispensaries located in the state. By 2024, Illinois should be capable of $1 billion-plus in annual marijuana sales.

In other words, patience should pay off handsomely for long-term investors.

A digital box with an illuminated cloud that's connected to and surrounded by circuitry.

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Fastly

If you have $10,000 at your disposal, high-growth edge cloud platform services provider Fastly (NYSE:FSLY) is another stock you'd be smart to consider buying.

Similar to Teladoc, Fastly has been a clear beneficiary of the COVID-19 pandemic. Businesses have had little choice but to create or bolster their online and cloud presence, and Fastly enables them to deliver content to end users quickly and securely. Brand names that use Fastly's edge cloud platform services include Pinterest, TikTok, and Etsy, to name a few.

But the Fastly growth story isn't just about landing new customers. The bulk of the company's operating margin expansion is going to come from existing clients expanding their needs for edge computing and security. In the recently ended quarter -- which, may I add, was one of the most challenging in history for the U.S. economy -- Fastly's dollar-based net expansion rate was 137%. This signifies that existing clients are spending more and staying with Fastly. 

Over the next three to four years, Fastly's sales are expected to more than triple. That's the type of growth long-term investors should want to buy into.

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Trupanion

Just saying the word "insurance" is enough to make some peoples' eyelids droop with boredom. However, you could rightly say that Trupanion (NASDAQ:TRUP) is a different breed of insurance company that has the potential to deliver sustainable double-digit growth for its shareholders.

Trupanion is a provider of health insurance for companion animals (cats and dogs). Between 1988 and 2019-2020, the American Pet Products Association notes that companion pet ownership has increased from 56% of all households to 67%. That's about 84.9 million households owning a pet today. What's more, U.S. pet expenditures haven't declined on a year-over-year basis in at least a quarter of a century, with an estimated $30.2 billion expected to be spent on veterinary care in 2020. 

Trupanion benefits on two fronts. First, it only has between 1% and 2% companion animal share penetration throughout North America. This means there's an incredibly long runway to educate pet owners about the benefits of insuring their four-legged family member.

Second, Trupanion has had two decades to build up rapport and clinic-level partnerships with veterinarians. Even with companion animal insurance expected to be a competitive space, Trupanion has clear-cut advantages and the ability to sustain a double-digit growth rate for a long time to come.

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.