There are a few fundamentals of investing that virtually everyone should follow, including diversification. It's one of the safest ways to ensure your portfolio is balanced and you reduce risk where possible.

Despite how important diversification is, it's OK to admit that not all stocks are created equal, and some have more of a special place in your heart (and portfolio). I'm no exception.

If there were only one stock with a special place in my heart that I would buy and hold for the long haul, it would be Microsoft (MSFT 0.59%). Here's why.

Microsoft is the technology one-stop shop

It's not uncommon for a big tech company to operate in different industries. However, none are as established in as many industries as Microsoft, a jack of all trades. Below are some areas it operates in:

• Productivity: Microsoft Office -- which includes Excel, Teams, PowerPoint, and Word -- has long been the standard for business and personal productivity tools.
• Cloud: Microsoft Azure is the world's second-largest cloud platform, with a 20% market share. It trails Amazon Web Services, with a 31% market share.
• Hardware: Apple rightfully gets a lot of praise for its hardware, but Microsoft's PCs and tablets are used by millions globally.
• Gaming: Xbox trails PlayStation in users and units but remains a force in the gaming industry. Microsoft's acquisition of Activision Blizzard should set it up for continued success.
• Social media: LinkedIn is the leading networking platform with over a billion users.

When I think of a stock I want to buy and hold, I look for one whose business doesn't rely too heavily on a single product, service, or (in this case) industry. Microsoft exemplifies that in the tech world.

Who Microsoft's customers are matters

Having a lot of customers is a great thing for any business, but who those customers are also plays a major role in a company's trajectory. In Microsoft's case, many of them are other companies.

Think about the many businesses globally that rely on its products and services. Countless companies issue PCs to their workers, Excel is a staple in the finance world, Cloud has become a vital part of modern business, and LinkedIn is a major recruiting hub. And that's just to name a few.

When the economy is less than ideal, individual consumers are more likely to cut back on spending than companies are. It's much easier for consumers to skip upgrading a smartphone than for businesses to cancel their cloud services or stop using tools like Excel or Teams. That's largely why Microsoft's financials have remained strong through recessions and similar economic downturns.

MSFT revenue (annual), data by YCharts.

This isn't to say Microsoft never hits any rough patches; virtually every business does if it's been around long enough. But if you're looking for a single stock to hold on to, you want a company built to endure these challenges.

A premium price for a premium company

Microsoft isn't cheap by most valuation standards, but that's to be expected. High-quality, high-visibility companies often command premium valuations. The stock is trading at around 32.5 times its projected earnings for this year, a little below its average for the past decade but in line with Apple at just under 33.

MSFT PE ratio (forward), data by YCharts; PE = price to earnings.

You shouldn't ignore valuations when investing, nor should you obsess over them if you're in it for the long haul. It may affect short-term returns, but when you look back a decade or more from now, chances are you won't be harping too much on the stock's price-to-earnings ratio at the time.

Warren Buffett said it best. It's far better to buy a wonderful company at a fair price than a fair company at a wonderful price. And with Microsoft, you know you're getting a wonderful company.