I carry a total of 23 tickers in my personal investment portfolio. The two largest holdings in it are streaming video giant Netflix (NASDAQ:NFLX) and e-commerce veteran Amazon.com (NASDAQ:AMZN) Both of these stocks have treated me very well over the years, and they happen to be great buys in today's market as well. These tickers will probably stay with me until I stop investing or the mullet becomes fashionable again, whichever comes first. (Hint: Trendy mullets are more likely than for me to hang up my Wall Street spurs.)

But if I had to liquidate it all and select just one stock for the long haul, I would actually go in a different direction. The only stock I would trust to meet all my investment needs forever is actually Google and Android parent Alphabet (NASDAQ:GOOG) (NASDAQ:GOOGL).

The core idea: flexibility equals longevity

Alphabet is my idea of a centennial investment.

I mean, both General Electric (NYSE:GE) and IBM (NYSE:IBM) have stuck around for a hundred years by constantly adapting to ever-changing market conditions. They survived technological revolutions, world wars, and lots of pitch-black recessions by ending business operations that no longer worked and replacing them with ideas better suited to the next challenge.

The keyword here is flexibility. GE and IBM have always had it in spades. Alphabet is no different.

Several arrows hitting the bullseye in a single archery target.

Image source: Getty Images.

Flexibility, defined

The company we now know as Alphabet used to be a one-trick pony. Sure, Google's online search and advertising empire is a pretty great trick, but the time will come when those operations just won't keep the lights on anymore.

Never afraid to tackle new business ideas -- big bets with uncertain outcomes such as the YouTube short-form video platform and the Android mobile phone system spring to mind -- the company rebranded itself as a collection of very diverse operations. It's true that Google-branded businesses accounted for 99.6% of Alphabet's total sales in the third quarter and all of the operating profits, but you have to start somewhere.

Alphabet is alpha-betting on a wide variety of mostly offline operations, from self-driving cars and medical research to drone-based delivery services and energy storage based on large tanks of molten salt. None of them are pulling their weight from a financial point of view, but some analysts expect the Waymo self-driving car service to become a $100 billion business in its own right, roughly a decade from now.

Most of Alphabet's non-Google stuff will probably fail to make a difference in the long run, but it is important that the company is exploring a plethora of new ideas at all times. One or two game-changing wins per decade should be plenty to keep Alphabet relevant, competitive, and profitable, effectively forever from the vantage point of one middle-aged human.

The upshot: You can trust Alphabet over the extremely long haul

There you have it. If I had to pick a single stock to power my portfolio all by itself for years and decades to come, Alphabet would be it. It's already a very large business but I'm convinced that we ain't seen nothin' yet.

I almost feel like I'm cheating a little because this single stock works as a play on lots and lots of different business ideas -- many of which we haven't even imagined yet. Alphabet's best days lie ahead, and we might even forget all about the ancient Google roots when all is said and done.

And that would be fine by me.

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.