In the three and a half months since the year started, investors have already seen quite a bit of volatility. Geopolitical tensions, economic issues, and interest rate hikes in the U.S. have contributed to the market's rather poor performance since January. Indeed, all three major U.S. market indexes are down as of this writing. 

But none of these issues warrant staying away from the stock market. Despite near-term headwinds, shares of robust companies will make it through -- and continue rewarding shareholders for many years. On that note, let's look at two excellent stocks that are worth buying and holding onto forever: Intuitive Surgical (ISRG -0.26%) and Johnson & Johnson (JNJ 0.84%)

Chart showing Intuitive Surgical's and Johnson & Johnson's total returns beating the S&P 500 since 2015.

ISRG Total Return Level data by YCharts

1. Intuitive Surgical 

Intuitive Surgical is a medical devices specialist best-known for the da Vinci system, a robotic surgical system that allows physicians to perform minimally invasive surgeries. There is a host of reasons why Intuitive Surgical has a bright future.

First, the healthcare industry is arguably on an upward path. Long-term aging trends will make the services companies in this sector provide even more invaluable in the coming decade. By 2060, roughly 25% of the U.S. population will consist of adults aged 65 and older. In 2019, this demographic made up just 16% of the U.S. population. The consumption of healthcare services tends to increase with age.

Second, Intuitive Surgical is an undisputed leader in the robotic-assisted surgery (RAS) market. The company held an almost 80% share of this space in 2020.

Physicians in an operating room.

Image source: Getty Images.

Minimally invasive surgeries confer health benefits to patients, including less bleeding, shorter hospital stays, and faster recovery times. That's why the RAS market will continue to expand, and Intuitive Surgical is well-positioned to benefit despite increased competition from other medical devices giants such as Medtronic.

One major reason Intuitive Surgical can remain atop this market for many years to come is that it boasts a solid, competitive edge. Healthcare facilities have to spend between half a million dollars and $2.5 million to acquire a da Vinci system. It also takes time to train medical staff on the machine. After spending all these resources on the da Vinci RAS system, switching to a competitor's system would be a costly proposition.

Furthermore, developing these machines is a complicated matter, not to mention the myriad regulatory hoops one needs to jump through. These barriers to entry ensure that newcomers have some serious catching up to do, and that's why Intuitive Surgical will continue to be dominant. The healthcare company has soundly outperformed the market in the past couple of decades. Expect that trend to continue for many years to come

2. Johnson & Johnson

As one of the largest pharmaceutical companies in the world, Johnson & Johnson will also benefit from the world's aging population, since prescription drug use increases with age. The company has a robust lineup of medicines that boasts multiple blockbuster products. Some of the top-selling ones of the bunch include cancer drugs Darzalex and Erleada as well as  immunosuppressants Stelara and Tremfya.

Last year, sales of Tremfya grew by 57.9% to $2.1 billion, while revenue from Stelara increased by 18.5% to $9.1 billion. Meanwhile, Darzalex reported sales of $6.02 billion, 43.8% higher than the year-ago period, and Erleada's sales of $1.3 billion soared by 70%. Johnson & Johnson's total sales for 2021 increased by 13.6% to $93.8 billion.

The company also has a rich pipeline with dozens of clinical programs. Investors can expect label expansions and brand-new products to bolster the company's lineup every year. Besides its pharmaceutical segments, Johnson & Johnson operates two other divisions: medical devices and consumer health. However, the company is currently spinning off its consumer health units -- home to famous and popular brands such as Neutrogena, Tylenol, Aveeno, and others -- into a stand-alone entity. The transaction should complete by the end of 2022.

Once it is done, Johnson & Johnson will be more focused on its pharmaceutical and medical devices businesses -- which typically record faster top-line growth rates than its consumer health units -- and the company will decrease exposure to hundreds of lawsuits related to some of its consumer health products.

In my view, this separation will work wonders for the company and its shareholders and constitute one more reason to add shares of the pharma giant to your portfolio. Last but not least, Johnson & Johnson is a Dividend King, having raised its payouts for 59 consecutive years. The company currently offers a yield of 2.35%, well above the average S&P 500 yield of 1.37%.

A strong position in a promising industry, a robust business, and an excellent dividend history make Johnson & Johnson worth parking in your portfolio for decades.