Time. We've all only got a finite amount of it, yet with every day that passes, many people miss out on the massive potential that compounding interest offers. They avoid investing in the stock market, thinking either that it's too risky, too unprofitable, or too complicated for them to ever understand -- and every day they delay, they're short-changing themselves of the potential to earn fantastic stock market returns by simply using time to their advantage.

In this clip, Motley Fool co-founder David Gardner explains why the stock market is the most powerful investing vehicle there is and goes through the numbers of why it's so vitally important to get started on your investment journey as soon as you (or your family, friends, and acquaintances) can.

A full transcript follows the video.

This podcast was recorded on Jan. 13, 2016. 

David Gardner: So my message this week is relatively simple, pretty direct. Here it is: get invested! I don't know that there's a more compelling and excellent achievement that I personally, and we here at The Motley Fool, can bring you and literally everyone you know to, to get invested. I think it's a fair presumption that if you're listening to this or any of our Motley Fool podcasts, you may be already are invested. Or if you're not yet invested, you do have a heart for it, you do recognize the importance of it. So I bet I'm preaching to the choir for many of our Motley Fool listeners this week when I say get invested. But if you already are, then of course, I'm going to urge you to think about the person in your family, the person who's closest to you, family or friend, who's not invested, and get them invested.

Help us all as Fools fulfill our purpose to get the whole world invested. Carpe diem, that's really the spirit of this phrase, certainly made famous to those who remember Dead Poets Society, that Robin Williams vehicle, I think it was the 1990s. It was one of the better movies of the 1990s. Carpe diem. In fact, I was doing a little bit of homework this week, it was Horace, the Roman poet, who in book one of his Odes, in exactly 23 B.C., first wrote the phrase carpe diem, but that's really the spirit of this week's message. 

The market averages about a 9%-11% historical annualized return. That's the American stock market's annualized return over the last century or so. Even if you're not confident that that will repeat itself over the next century -- and I think it's a perfectly valid expectation that it will -- but, even if you think, "Ah, 9% sounds high, everything's maturing, we're getting more of a global village, a more mature, global economy," maybe 6%, you know what? With inflation at about 1%, your real return of 5%, if that's your lower expectation, is still so compelling, if you just play the math forward of being invested. It's such a good place to be. And you think about all of those people who either are without capital because they haven't effectively saved, or maybe they do have capital, but it's just sitting there, uninvested or underinvested for the long term. Get invested! Seize the day.

Here's some numbers. If you get started early, the earlier you get started, let's take $1,000 per year at the age of 20. So a 20-year-old investing $1,000 per year for 45 years, that will come at an 11% annualized rate to $986,600. Again, 45 years, from age 20 to age 65. You just invested -- do the math with me -- $1,000 per year. You just invested $45,000. And you never even increased it beyond that $1,000, for this simple mathematical example: You just kept it invested, and $986,600 is where you come out. And your money was working for you. You weren't having to work that hard.

Now, by contrast, let's instead take a 45-year-old today, and let's see how the 45-year-old gets to 65. Let's say it's the same 11% return. Let's say the 45-year-old has $3,000 to put away per month in earnest, more money than a 20-year-old would have -- $3,000 per year, ages 45 to 65, that comes to $192,600. You invested $60,000, and you ended up with about $190,000 by age 65 when you waited 25 years to start. Get invested!

You know, if you invest just $100 per month for 30 years at that same 11% rate, you're going to end up with $280,450 -- $100 per month. At a 9% rate, by the way, because 11% is on the higher end of most people's expectations, at a 9% rate, that's still $183,074. I've got my calculator out this week. If you invest just $150 per month, so, just jack it up $50 more, and earn 15% per year -- which, by the way, is below Motley Fool Stock Advisor's annualized return in the 12-year history of our service -- you're going to end up with more than $1 million. 

There's an interesting site, if you've been to New York City, or maybe lived there, but, at any time in the last couple decades. I can't even identify where in Manhattan it is, because I go through the city perhaps four or five times a year. But there's somewhere there, there's a calculator that is showing our national debt. And if you've seen this, it's kind of a big billboard positioned somewhere, I think it's in the lower half of Manhattan, it's showing, constantly, numbers running up, because, of course, our national debt is ever-increasing. So you just sit there in real time and you're watching the money count up, and it makes quite an impression on you. It's a fairly compelling site. I don't even know whose billboard it is. And I'm assuming it's still there, but if it isn't, it was there for a good 15 years or so, and it's still counting up, whether it's there or not.

But let's change contexts for a second. Let's pretend that that amount of money isn't running up, but running down. And it's not the federal debt, it's actually your future net worth, because for every second, literally, that you wait to get invested with money, your future expected net worth is declining. I hope that's not taken as a dreary message. I hope it's a carpe diem message. I hope, even though I bet you've already started the power of the compounding clock in your life as an investor, as you cast your eye about those around you, at work, at home, in the marketplace, please do feel free to see that image of money, net worths, counting down constantly, for anybody around you who is not invested. 

Again, there are very few things that return even 5% or more per year. The stock market has done about double that over the course of the last century. It's sad, sometimes, to think how market coverage makes it sound scary, makes it sound like a great big gambling machine, or, for a lot of people, they think they'll never figure it out. To think how many people are not becoming part of our ownership culture, who don't have the benefit, simply because they didn't have somebody to tap them on the shoulder and get them clued in, maybe right around January of each year, to think about how important and valuable it is in their life to be part of the game and not sitting outside of the game.

So there you go. There's a mental image for you. Picture that Manhattan billboard, but it's counting down for every second that anybody you know waits to get invested in the compounding power of the stock market.

Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.