I own more than 20 stocks, and have no plans to sell any of them anytime soon. Even the handful of stocks in my portfolio that are underperforming right now still have solid long-term potential, in my view. However, I wouldn't totally rule out selling some of these stocks.

There are a few stocks that I currently own, though, that I'll probably never sell. Here's why Alphabet (GOOG -1.91%) (GOOGL -1.80%), Walt Disney (DIS 1.26%), and Intuitive Surgical (ISRG 0.03%) belong in that category.

Three golden eggs in a nest made of $1 bills

Image source: Getty Images.

1. Alphabet

No economic moat is completely impenetrable. But Alphabet's moat is pretty close to it. The company could be the poster child for the network effect -- a competitive advantage stemming from a product or service becoming more valuable as more people use it. Alphabet claims eight products that each have more than 1 billion users every month.

The world's biggest company right now, Microsoft, tried to challenge Alphabet's Google Search by launching its own Bing search engine several years ago. What was the outcome? Bing gained market share. But it didn't hurt Google Search, which also gained market share. If Microsoft can't dethrone Google, I don't think anyone can.

This market dominance translates to tremendous cash flow. When a company can generate strong cash flow for as far as the eye can see, I think its stock is a stock to keep. Also, companies that deliver strong cash flow tend to have plenty of money to invest in growth. Alphabet certainly fits the bill.

I like Alphabet's investments in both Calico, its subsidiary focused on prolonging human life, and Wing, another subsidiary that has developed drones for delivering packages. My favorite, though, is Alphabet's self-driving-car technology subsidiary Waymo. UBS analyst Eric Sheridan predicts that Waymo could be a $100 billion business by the end of the next decade. I suspect he could be right.

2. Disney

In June I wrote about 12 reasons to buy Disney stock and never sell. I won't repeat all 12 reasons here, but a few are especially worth noting. Near the top of the list is Disney's strong cash flow.

I also view Disney's brands as a powerful and sustainable competitive advantage for the company. Among consumers in the major markets where Disney operates, 95% are familiar with its brands. And more than 1 billion people across the world call themselves Disney fans. I don't think Disney will have any problems attracting customers during my lifetime.

In the entertainment world, it's often said that "content is king." You might say that Disney is the ruler of content: The company has made more than 740 movies and counting, and its acquisition of Twentieth Century Fox adds even more movies to its arsenal. Disney also owns the content from shows that have aired through the years on its networks, including ABC, Disney Channel, and ESPN.

My take is that Disney has multiple huge growth opportunities. It's launching the Disney+ streaming service this year. Millennials should begin having more kids, which will drive demand for a wide range of Disney products and services. And the middle classes are growing in developing nations, potentially expanding Disney's global market. Simply too many good things could happen for Disney for me to think about selling this stock.

3. Intuitive Surgical

Intuitive Surgical isn't the household name that Google and Disney are. But like both the companies behind those brands, Intuitive has a very strong moat -- this one in the robotic surgical systems market.

In 1999, Intuitive Surgical launched the da Vinci robotic surgical system. Since then, subsequent generations of da Vinci have expanded the market for robotically assisted surgery. Intuitive dominates this market with a track record that no other company can match.

I really like Intuitive's razor-and-blades business model. The company makes over 70% of its total revenue from recurring sources -- instruments and accessories that must be replaced after surgical procedures are performed using da Vinci. Intuitive's recurring revenue percentage should continue to rise as more customers opt to lease systems rather than purchase them. This, of course, ensures that the company will keep on generating that strong cash flow that I love.

What about growth opportunities? Intuitive Surgical has a lot of them. Long-term demographic trends should drive more demand for procedures that are well-suited for robotic surgery. Innovation should expand the types of procedures for which robotic surgery can be used. Intuitive also should have significant opportunities to increase sales in international markets.

Never ever?

Never is a very strong word. Is there any chance that I could sell Alphabet, Disney, or Intuitive Surgical stock in the future? Sure. If something significantly undermined the reasons why I like these stocks so much, I could sell them.

The important point, though, is that I don't see that happening. My view is that Alphabet, Disney, and Intuitive Surgical will be able to sustain their competitive advantages and deliver solid growth over the long run. Stocks like that are the ones you want to buy and never sell.