Fifty-five percent of the adult population in the U.S. is invested in stocks, according to Statista. It's not unreasonable to conclude that all of these investors understand the importance of investing in stocks. Yet just buying stocks doesn't guarantee success.  

To succeed at investing, you must pick your stocks carefully, and buy and hold them for as long as you possibly can. Adding growth stocks to your portfolio, for instance, could grow your wealth exponentially over time, especially if these stocks are riding megatrends. Here are four such compelling growth stocks you can buy now and hold forever. Each one is a bet on an unstoppable trend.

E-commerce potential is bigger than you think

The convenience of shopping online wasn't lost on anyone, but the physical distancing necessitated by the COVID-19 pandemic has compelled more people than ever to shop online, especially in erstwhile less popular categories like groceries.

To give you an example, the online grocery market in India is projected to hit nearly $18 billion by 2024 from only $1.9 billion in 2019. As someone from India, I can vouch for the growth in e-commerce. I am among the many consumers who rarely purchased online until last year; but now, I have multiple subscriptions.

A person putting money into one of four savings jar for large purchases like a house.

Image source: Getty Images.

India is just one example. eMarketer projects the global e-commerce market will hit $4.9 trillion this year and nearly $6.4 trillion by 2024 from $4.3 trillion in 2020. E-commerce penetration in the U.S. alone could more than double between 2020 and 2025, according to eMarketer. Clearly, this is a booming market, and you'll likely make good money investing in a stock like Shopify (NYSE:SHOP), which enables merchants of all sizes to set up online stores and sell products through multiple sales channels, earnings subscription and value-added fees in return.

Shopify is firing on all cylinders, racking up gross merchandise volumes worth a whopping $42.2 billion in its second quarter and crossing the $1 billion revenue mark in a quarter for the first time ever. For perspective, Shopify's 2020 revenue was $2.9 billion, up 86% from 2019.

There's tremendous potential as Shopify continues to roll out newer features and services to expand its merchant and customer base beyond the U.S. Shopify has been a high-growth stock, and I doubt it will stop being one anytime soon.

SHOP Chart

SHOP data by YCharts

A surefire bet on one of the world's biggest trends

No megatrend is attracting as much attention as clean energy, and rightfully so: The threat of catastrophic climate change is forcing nations to decarbonize and build a cleaner future. And this clean energy revolution is only getting started, which means if you invest in renewable energy stocks with global reach and a proven growth strategy, you could be sitting on big money in just a few years. Brookfield Renewable (NYSE:BEP)(NYSE:BEPC) is a perfect choice.

On Sept. 8, the Department of Energy released a study showing how solar and wind energy combined could supply 75% of the electricity needs in the U.S. by 2035, with solar taking the lead thanks to its low cost. Brookfield Renewable is primarily into hydropower but is expanding full force into solar and wind. CEO Connor Teskey recently said he sees "no limitation to the amount of growth" the company could pursue in solar given that it's the fastest-growing renewable source in the world today. Management even recently projected a "majority" of the company's production capacity could come from solar within a decade.

Brookfield Renewable has years of experience and the backing of parent organization Brookfield Asset Management (NYSE:BAM) to make the most of the opportunities in renewable energy. In fact, its development pipeline of nearly 31 gigawatts (GW) far exceeds its current capacity of 20 GW and is already enough to power growth for years to come. Brookfield Renewable expects to grow funds from operations (FFO) per share by up to 20% through 2025 and dividends by 5% to 9% annually.

BEP Chart

BEP data by YCharts

If 10% compound annual growth in FFO and 6% growth in dividends between 2010 and 2020 could generate such big returns for Brookfield Renewable shareholders, the sky could be the limit for investors willing to own the stock for decades.

There could be no upside limit to this multibagger stock 

Upstart Holdings (NASDAQ:UPST) is largely a bet on two megatrends, and it combines the best of both worlds as a fintech company using cloud-based artificial intelligence (AI) to disrupt the lending market.

Upstart doesn't lend money but uses AI to screen borrowers and originate loans for partner banks, and earns fees in return. As much of the process is automated, consumers can apply for loans easily with high approval rates. For banks, Upstart can help expand their customer base and reduce loss rates as it uses 1,000 or more variables and a history of more than 10 million repayment events to screen borrowers. Upstart's network of institutional investors also fund support for banking partners through secondary loan purchases.

A promising technology that has already found several takers, it had 12 bank partners in December 2020. Upstart is growing at an astounding pace as the following data from its last quarter illustrates:

  • Revenue shot up 1,018% to $194 million.
  • Net income came in at $37.3 million versus a loss year ago.
  • Loans originated jumped 1,604% to $2.8 billion.

Now here's something to ponder: If Upstart can attain such stunning growth numbers just from personal loans, imagine what it could do once it enters new verticals. It has, for example, entered the much bigger auto loan space after acquiring Prodigy Software, and has already tied up with five banks. Auto loan origination volume in the U.S. was $635 billion between Q2 2020 and Q2 2021 compared with $84 billion origination in personal loans.

Upstart is already profitable and expects to generate revenue worth $750 million in 2021 versus $233.4 million in 2020. Yes, it's already had a dizzying run-up this year, but think long term: With such huge addressable markets, Upstart shares could boom in coming decades. 

This stock could hit $100 billion as the industry explodes

The COVID-19 pandemic has changed our lives in many ways. Perhaps the biggest trend it may have kicked off is virtual healthcare, or taking medical consultations online without having to step out of our homes. Teladoc Health (NYSE:TDOC) recognized the opportunity before anyone else and is the world's largest virtual-care service provider today. Yet the company's growth has only just begun.

Industry experts project the virtual-care market will grow double digits in coming years, with Frost & Sullivan even predicting the U.S. virtual-care market will grow sevenfold by 2025. That may sound ambitious, but even if the markets can grow by half that much, Teladoc could end up making a substantial amount of money.

Teladoc was already the leading virtual-consultations provider before it leaped into chronic-disease management by acquiring Livongo Health last year. The global chronic-disease management market alone could be worth $6.5 billion by 2027, up from $3.6 billion in 2020.

Teladoc is already growing at a rapid pace: Its revenue more than doubled last quarter, and with management projecting $2 billion in revenue this year, Teladoc will have almost quadrupled its revenues in just two years!

Teladoc is seeing strong growth in various verticals like mental health and non-infectious diseases, and expects to register 13.5 million to 14 million visits this year, up from 10.6 million visits in 2020. Given its pace of growth and market opportunities, I wouldn't be surprised if Teladoc shares hit a market capitalization of $100 billion as early as 2026 from the current level of $22.7 billion.

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.