Arguably the three most important words in investing are: I don't know. Acknowledging that you don't know for sure what will happen with any investment can save you from a heap of trouble. 

However, this doesn't mean you can't have strong opinions about certain investments. I'm quite confident that some stocks will be winners over the long run. Here are my three highest-conviction growth stocks to buy in 2025.

1. Amazon

Few companies enjoy as strong of a competitive moat as Amazon (AMZN 0.01%). Actually, Amazon has multiple strong moats. There's a networking moat with the company's e-commerce platform becoming increasingly valuable as more customers and sellers use it. Amazon's size gives it a scale of operations moat. And there are more.

Amazon's competitive advantages span across its businesses, too. The company is the 800-pound gorilla in e-commerce. Its Amazon Web Services (AWS) ranks as the top cloud services provider.

What I like the most about Amazon, though, is that the company doesn't rest on its laurels. Founder Jeff Bezos instilled a culture with a mindset where every day is "day one." In other words, Amazon strives to always think like a start-up -- looking for ways to grow.

Although Amazon is now a $2.3 trillion giant, it still has multiple ways to grow. Artificial intelligence, especially generative AI, is driving organizations to shift their IT spending to the cloud. E-commerce remains only a fraction of the overall retail market. Amazon has expanded into new areas as well, including groceries, healthcare, and robotaxis. 

I'm cautiously optimistic that Amazon stock will again deliver solid returns in 2025. But I'm very optimistic that it will deliver market-beating gains over the long term.

2. Nvidia

I'll readily admit that I have underestimated Nvidia (NVDA -0.02%) in the past. To be more specific, I underestimated just how much the demand for its graphics processing units (GPUs) would skyrocket. However, I'm decidedly upbeat about Nvidia's future now.

Jensen Huang, Nvidia's founder and CEO, believes that the company's new Blackwell GPU platform could become the most successful product in its history. Huang even thinks Blackwell could become the most successful product in the history of computing. I believe he's 100% correct on the first point, although the jury is out on the second one. 

We'll soon see the first Blackwell revenue hit Nvidia's books. The chipmaker will almost certainly post record revenue each quarter of 2025. I expect the momentum to continue into next year, too.

Nvidia's rapid pace of innovation is what really undergirds my high conviction about the stock, though. The company plans to roll out new technology every year. Blackwell probably won't hold the distinction of being Nvidia's most successful product ever for very long. 

3. Vertex Pharmaceuticals

Because of the inherent risks that all drugmakers face, Vertex Pharmaceuticals (VRTX 0.93%) might seem to be an unlikely candidate for my list of highest-conviction stocks. However, I have liked this biotech stock for years and believe it's on the cusp of delivering tremendous gains.

Vertex's success thus far has been driven by its cystic fibrosis (CF) therapies. I predict even brighter days ahead for the company in CF now that it has secured U.S. Food and Drug Administration (FDA) approval of Alyftrek. This therapy was better than Vertex's blockbuster drug Trikafta in clinical studies and offers a more convenient once-daily dosing. To add icing to the cake, Vertex will pay lower royalties on Alyftrek than it does on its other approved CF therapies. 

The company is also expanding beyond CF. The commercial launch of Casgevy is gaining momentum. This gene-editing therapy is a one-and-done treatment for the rare blood disorders sickle cell disease and transfusion-dependent beta-thalassemia. Vertex awaits FDA approval of suzetrigine in treating acute pain, with a decision expected this month. 

More powerhouse therapies could be on the way. Vertex is evaluating three other programs in pivotal clinical studies. Inaxaplin targets APOL1-mediated kidney disease. Povetacicept is an experimental treatment for another kidney disease, IgA nephropathy. The company is even testing a potential cure for type 1 diabetes with VX-880 and a successor in phase 2 testing, VX-264. 

I'm not 100% sure all of Vertex's pipeline candidates will be successful. However, I think most of them will be. And I expect this already big biopharmaceutical company will grow much larger over the next decade.