The only way to make money with stocks is to buy low and sell high. That's it. There are no rules that say how long that period has to be between when you buy and when you sell. We all have those one or two stocks in our portfolio that we refuse to sell, though, because the future returns are better even if they net a decent return today.

So we asked three of our investing contributors to highlight stocks they refuse to sell. Here's why they picked (NASDAQ:AMZN), General Motors (NYSE:GM), and Enterprise Products Partners (NYSE:EPD)

One person refusing cash from another person

Image source: Getty Images.

I'm riding this wave as far as it can go

Brian Stoffel ( Last year, my wife and I bought our first house. I mention that because in order to pay for it, we had to sell some shares of Amazon. That has been -- and I fully intend for it to remain -- the only time we part ways with shares of the company for the next few decades. Currently, the stock makes up a -- perhaps (small f) foolish -- 21% of my real-life holdings.

It's important to note that I didn't intend for it to be this way: Only 4% of all the cash we've invested in the stock market has gone toward Amazon. The position has just grown to be that large.

But there are two big reasons I don't intend to ever sell shares of the company. First, it has an enormous moat around it. The company's network of fulfillment centers is unmatched both domestically and abroad. It would be prohibitively expensive for competitors to match Amazon's reach, meaning that few will ever be able to offer the quick delivery and convenience that Amazon can.

Furthermore, the company has started to benefit from powerful network effects. As Amazon Prime membership rolls swell, third-party vendors are realizing that by signing up for Fulfillment by Amazon, they'll have access to a greater audience. That, of course, draws in even more Prime members -- creating a virtuous cycle.

But perhaps most important is the company's willingness to fail. By taking on dozens of expensive experiments every year, the company is bound to hit on one or two that truly move the bottom line -- like Amazon Web Services, Echo, and the like. It's that type of approach -- which yields multiple futures -- which leads me to believe that Amazon will soon be a trillion-dollar company.

An old company taking a brand-new approach

John Rosevear (General Motors): The U.S. new-car market is probably past its peak. New high-tech ideas and entrants are threatening (credibly) to upset the traditional auto business in ways that could make car ownership a thing of the past for many.

As the Fool charged with covering the convergence of tech and autos, I know all of this as well as anyone. So why am I hanging on to crusty old General Motors?

Here's why: GM isn't crusty-old-GM anymore. This GM is a growth-minded, tech-savvy powerhouse. It's not easy for casual observers to see, but the reality is that CEO Mary Barra and her team have completely rethought GM, dumping old money-losing businesses and doubling down on high-growth opportunities.

What makes me want to hang on to GM is the combination of priorities put in place by Barra and her team: First, look for the best possible returns on capital, and, second, go big on potentially disruptive technologies before GM itself can be disrupted by outside forces. Eventually, the market is going to see what I see: GM is going to be a big player, with growing profits, for a long while yet. 

If you add in GM's solid and sustainable 4.2% dividend, maybe you'll see why I'm determined to hang in for the long haul. 

I'm holding this one to build wealth with dividends

Tyler Crowe (Enterprise Products Partners): I'm probably not like most master limited partnership investors. These high-yield investments are typically found in portfolios of people looking to supplement their income. I'm not looking for income right now. I'd like to think that I'm a younger investor with the time to let slow-growth, high-yield investments build wealth through very long time horizons and consistently reinvesting dividends. Enterprise Products Partners is a stock that is built for this kind of investment strategy.

Enterprise owns and operates 50,000 miles of pipelines, 260 million barrels of storage, 18 export terminals, and 60 treatment and petrochemical facilities. While this network covers all types of hydrocarbons, Enterprise's claim to fame is natural gas liquids (NGLs) and network connectivity. NGLs are used in the crude refining process, petrochemical manufacturing, and heating products such as propane. Enterprise can deliver to meet all of these types of demand with a network that connects to every major shale basin in the U.S., 90% of America's refining capacity east of the Rockies, and every ethylene cracker treatment facility in the country.  

This highly connected system gives Enterprise lots of different levers to pull to grow the business at a slow and steady rate. It also helps that more than 85% of the company's revenue comes from fixed-fee services that ensure stable cash flows from quarter to quarter. These factors all translate to steady dividend growth for the past 20 years and have a good chance of maintaining that payment growth streak for another 20 years. If I want to build wealth over the long term, putting Enterprises' 6% distribution yield to work for several decades should help me achieve that goal.

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.