What are the most difficult things about investing? For many people, accumulating money to invest in the first place would probably top the list. Another biggie is finding the right stocks to buy. Perhaps the most challenging thing for most investors is having the patience to wait for stocks to deliver on their full potential.

You'll have to work on accumulating money to invest and building patience on your own. But if you've got those bases covered, there are several great stocks you can buy. Here's where to invest $10,000 right now to achieve huge gains over the long run.

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Brookfield Renewable Partners: A future-proof stock

Future-proof. That's how Brookfield Renewable Partners (NYSE:BEP) describes itself. And that description is spot on, in my view.

Brookfield Renewable ranks as one of the top renewable energy stocks. It owns hydroelectric, wind, and solar facilities across Asia, Europe, North America, and South America. These facilities combined generate over 19,000 megawatts of electricity. The company also claims a development pipeline with 13,000 megawatts of capacity.

I think Brookfield Renewable truly is a future-proof stock because the shift toward renewable energy appears to be unstoppable. It's not just that many countries target aggressive goals for renewable power generation. It's not just that renewable energy generation is better for the environment. Renewable power -- particularly wind and solar -- has become more cost-effective than fossil-fuel energy sources.

Brookfield Renewable boasts a virtually guaranteed path to growth. The company expects to deliver average annual returns of between 12% and 15%, with part of those returns given to shareholders as dividends. An initial investment of $10,000 would double in only five years at the upper end of that growth range. 

Fastly: Its name says it all

Fastly (NYSE:FSLY) picked the perfect name. You're not going to find the word "fastly" in any dictionary. But it's applicable to both Fastly's business and its stock performance

The company markets technology that speeds up the delivery of apps and data on the internet. Fastly's edge computing platform moves processing closer to the cloud's "edge" -- the point where corporate networks connect with the cloud. Its content delivery network (CDN) platform distributes web servers geographically to deliver content more quickly to end users.

With the COVID-19 pandemic driving more business and work online, edge computing and CDN has become hotter than ever. So has Fastly stock: Its share price has nearly quintupled so far this year. But should you be worried that Fastly now trades at a nose-bleed valuation of more than 38 times sales? I don't think so.

Edge computing and CDN should together be a $35.4 billion market by 2022. And this market will become even bigger throughout the rest of the decade and beyond. Fastly appears poised to continue capturing more of these two fast-growing markets. With a market cap still in the ballpark of $10 billion, this sizzling stock still has a lot of room to run.

The Trade Desk: The future of advertising has arrived

You no doubt see many digital ads every day. They're on websites. They're on apps. They're also increasingly on connected TV (CTV), thanks to the rise in streaming TV services. What you don't see, though, is how the underlying process for buying and selling those ads has been transformed. The future of advertising has arrived. And The Trade Desk (NASDAQ:TTD) stands at the center of it all.

The Trade Desk provides a technology platform for advertisers and ad agencies to buy digital ads online. This business model, called programmatic advertising, is much quicker and more cost-effective than the old-school way of buying and selling ads, which involved negotiations with media outlets.

Sure, some advertisers could reduce their budgets in the aftermath of the COVID-19 pandemic. However, the viral outbreak is also driving CTV usage higher. The Trade Desk's year-to-date gain of more than 70% shows which impact has been greater.

The programmatic advertising market is currently only a sliver of the total ad market. But it's growing five times faster. CTV is pouring fuel on the fire of an already big shift to digital ads. The Trade Desk wins from both trends. I think it's a stock that could triple or more within the next decade.