To say I will never sell a stock typically means one of two things: either management has laid out a strategy that obviously compounds its advantages over time or the company is benefiting from a trend that has no end in sight.

For Markel (MKL 0.66%), management evaluates itself in five year windows and is transparent about its methodical approach to deploying capital. It is also following a model that has proven itself over the past half century. On the other hand, Rollins (ROL -0.84%) is riding a wave of climate change that is making its service valuable in an ever larger portion of the globe. Both give me good reason to suspect I'll never sell a share.

A man in a suit holding up a golden egg with a clock on the wall behind him.

Image source: Getty Images.

1. Markel

Markel is a specialty insurer that has developed an expertise in pricing unconventional risks. By focusing on areas like Arabian horses, summer camps, and karate schools, it has carved out a niche for itself where competition isn't fierce and its experience allows it to accurately assess the fair price for an insurance policy.

That expertise shows up in the combined ratio. It's the percent of premiums collected that insurers pay as claims. Similar to gross margin, it is the standard measure of policy profitability. Anything under 100% means the company made more money than it paid out. For the past 15 years, Markel has only had two years where its combined ratio exceeded 100%. For that decade and a half, it averaged 95%. For context, the industry average is 100% -- break even -- over the past five years.

That profitability has allowed management to invest in equities and buy small businesses. It's why many think of the company as the baby Berkshire Hathaway (BRK.A -0.01%) (BRK.B -0.09%). Like Berkshire, Markel uses book value per share as a yardstick for the company's value. It has grown 10.6% annually over the past decade, from $334 to $914. To underscore its long-term approach, the company uses five year time frames to evaluate its performance. And it is honest when it doesn't measure up.

Management pointed out in the most recent shareholder letter that the stock hasn't delivered over the past half-decade. At the time that letter was written, shares had underperformed the broader S&P 500 index by an eye-popping 6,680 basis points since 2015 (100 basis points is equal to one percent). So far in 2021, the stock has merely held steady versus the index. It's a far cry from what shareholders had experienced over previous periods.

Period Markel Shares S&P 500 Annual Outperformance
2006 to 2010 19.3% 0.8% Markel by 3.5%
2011 to 2015 133.6% 62.5% Markel by 11.3%
2016 to 2020 17% 83.8% S&P 500 by 10.8%
2021 YTD 14.6% 13.4% Markel by 1.2%

Data Source: Y-Charts; YTD=Year-to-Date.

Over the entire 15 year period, Markel shares are only slightly outperforming. With stock valuations near the highest ever recorded by some measures, that trend of mediocrity is unlikely to persist for the next decade.

MKL Chart

MKL data by YCharts

2. Rollins

Rollins can trace its roots back to a small pest control business in the late 19th century. These days, it has 2.8 million customers across 900 locations worldwide. The last few decades have proven that getting rid of unwanted pests and wildlife is not something people cut back on even when the economy struggles. Rollins has seen 23 consecutive years of revenue growth and has averaged 20% annual earnings growth over the past two decades. That's not likely to change.

The company has a pristine financial profile, with immense cash generation and little debt. But what convinces me to hold for the next few decades is the impact a warming climate will have on the pests Rollins makes its money removing. A few examples prove the point.

Cockroaches love the hot humid air during summer. It's their breeding season. As the temperatures rise, they also get more active. In fact, they even cover more territory. Although they don't move much when it's cold, they begin to walk and run when it heats up. Real migration can happen when the temperature climbs above 100 degrees Fahrenheit -- they take flight. If you are expecting dry conditions to stand in the way of their progress, think again. Unlike humans, they can hold their breath for 40 minutes at a time in arid conditions to prevent dehydration.

Warmer winters and hotter summers also provide a great breeding environment for rats. With a gestation period of only 14 days, and an ability to start reproducing at only one month old, one pregnant rat can lead to more than 15,000 babies in a year. That's both impressive and disgusting. With global temperatures rising, rats brazenly meandering towns and cities like they did during the COVID lockdowns could become more prevalent.

Another result of rising temperatures has been an increase in mosquito-borne illnesses. Scientists believe over the next 30 years, the bloodsuckers will expand their territory to reach half of the world's population. Recent data suggests various species are spreading north at about 37 miles-per-year in the U.S. and 93 miles-per-year in Europe. Although there are multiple factors behind the migration, it all adds up to an expanded opportunity for Rollins. It's a change that will occur over the next 30 years. For me, it's a good reason to hold shares and never sell.