Part of the joy of investing is seeing your good investments continue to grow, years after your initial purchase. Aside from the financial satisfaction that you get from seeing a stock's value rise over time, you also get to savor that oh-so-precious feeling: I was right

Once you've had enough self-congratulation, you can always choose to sell the stock and lock in your gains. But, if you're like me, there are a few stocks that just keep on giving so reliably that you'll never let them go. If you're looking to invest in something for the long haul, you'll probably be interested in these stocks too.

A stopwatch rests on a $50 bill.

Image source: Getty Images.

1. AbbVie

As a major pharma company, AbbVie (NYSE:ABBV) delivers for its investors by developing and commercializing new drugs, like its best-selling arthritis treatment Humira. There's two reasons AbbVie is worth holding forever: its skill with drug development, and its generous dividend. The dividend hasn't ever been cut, and it's been increasing steadily over time. Right now, the forward yield is around 4.7%. But how does the company pay for it?

That's where things get much more interesting. Like many other pharma companies, AbbVie maximizes the revenue that it gets from each of its drug development projects by investigating their usefulness for multiple illnesses. Then, when it finds a promising lead, it runs a clinical trial to get regulatory approval for new illnesses other than what the drug was originally approved for. Case in point: For Humira, the original regulatory approval to treat arthritis in 2002 was only the very beginning of its revenue potential. Since then, it's been approved to treat eight (!) additional conditions, making the company $19.2 billion in 2019 alone. 

Humira isn't the only therapy that AbbVie has worked hard to expand. Its monoclonal antibody risankizumab for psoriasis and upadacitinib for arthritis will likely follow a similar trajectory with their approved indications and revenue potential over time. It's this organizational talent for making its products increasingly lucrative over time that makes AbbVie worth holding forever. Where other companies might try to get their drugs approved for one or two other indications after launch, AbbVie never stops investing in its winners, and its shareholders tend to benefit as a result.

2. Abbott Laboratories

Abbott Laboratories (NYSE:ABT) is another healthcare stock that I'll hold forever. It sells consumer healthcare goods like Pedialyte, as well as medical devices like pacemakers, glucose monitors, and catheters. It also offers a plethora of medical diagnostic tests and medicines, not to mention surgical tools like cardiac stents. If you can't see a trend yet, don't worry -- Abbott's appeal is that it sells a huge swath of critical healthcare products to many different markets. Many of these goods don't require any additional investment to keep selling year after year, which means that Abbott can invest its funds to make new products to add to its repertoire. This flexibility came in handy during the COVID-19 pandemic, when Abbott was able to create several different coronavirus diagnostic tests that went on to become best-sellers nearly overnight.

SPY Total Return Level Chart
Data source: YCharts.

Importantly, Abbott Labs has profitably repeated its formula of making evergreen healthcare products for decades and decades on end. Like AbbVie (which is actually one of its spin-offs), its dividend (with a current yield of 1.6%) has increased over time, and its payment is quite sustainable, given its rapid quarterly earnings growth of 28.3% year over year. 

In summary, I'll never sell Abbott Laboratories because I expect that it'll continue to innovate and expand its durable revenue base indefinitely. While its dividend will never make you rich, it sometimes ratchets upward by a significant amount, and the stock is a case study for why you should invest for the long term. Compared to the wider market, the total returns for shareholders have been much better with Abbott for at least the last decade. I fully expect this trend to continue, so I'll be sure to keep holding.

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.