The COVID-19 novel coronavirus pandemic has rocked the stock market, with the Dow Jones Industrial Average and S&P 500 index both down more than 30% from their highs, and many individual stocks performing much worse than that.

I've generally been a believer in Warren Buffett's often-cited investment advice that it's smart to be greedy when others are fearful. And to say that there's fear in the markets right now would be a massive understatement.

However, in the midst of the turbulence in the stock market could be some excellent opportunities for investors who measure their returns in terms of decades, not months or even years. And that's why I've added beaten-down stocks Stitch Fix (SFIX -0.89%) and Goldman Sachs (GS 0.64%) to my portfolio since the market downturn began.

Finger pressing a red buy button

Image souce: Getty Images.

Social isolation could help this beaten-down e-commerce company

Stitch Fix's latest numbers (released a little over a week ago) were actually quite impressive on the surface. Revenue grew 22% year-over-year and the company reported 3.5 million active clients -- 17% more than a year ago. What's more, the company's existing customers continue to spend more money as time goes on.

That was the good news. Unfortunately, Stitch Fix significantly cut its full-year revenue and adjusted EBITDA guidance. It's not a terrible situation. The company still expected revenue to grow, just not as much as it previously thought.

The results were enough for the stock to lose about 40% of its value, and I jumped at the chance to add it to my portfolio. Stitch Fix has an excellent management team and tons of growth runway and could actually get a short-term boost while Americans are maintaining social distancing and avoiding malls.

A great play on banking in an uncertain environment

Bank stocks have been one of the hardest-hit parts of the stock market, mainly due to a combination of plunging interest rates and an expected uptrend in loan defaults caused by the coronavirus' economic fallout.

With the stock about 40% off its highs, I finally pulled the trigger and added Goldman Sachs to my portfolio. While certain areas of Goldman's business are certainly likely to suffer, such as its asset management, M&A advisory, and its loan portfolio, there are still plenty of reasons to like Goldman for the long run.

For one thing, its consumer banking division -- which includes the Marcus saving and lending platform and the Apple Card credit card business, for now -- has plans to expand into checking accounts and investments. Also, the recent stock market volatility could actually give Goldman a boost to its trading revenue, which is a big part of the company's business.

Too early?

When I've told people that I've been buying stocks over the past few weeks, the most common reply I get is "you're too early -- it's going to go down even further," or other comments to that effect. And to be fair, they might be right. The bear market could certainly get far worse before it gets better.

However, I'm not worried. For one thing, these are three well-run companies that have lots of growth trajectory going forward. I liked these three companies before the downturn and jumped at the opportunity to get in at a discount.

And even if I am "too early" on them, that's OK. Historically speaking, buying the stocks of great companies when the market was 25% or more off its recent highs has been a great entry point for long-term investors.