Most of us are pretty good at coming up with excuses while we put off doing important things. Our tires might need more air, for example, but it looks like rain today, so maybe we'll aim to fill them tomorrow. We should go for a walk or run, but it's very hot out.

Excuses abound with our finances, too. We're often not saving, investing, and building a more secure financial future for ourselves because of various excuses -- and that can have devastating consequences, if we enter retirement unprepared. Here's a look at many common excuses, along with why they don't hold water:

A young man is pointing to himself, surprised.

Image source: Getty Images.

Excuse No. 1: I'm still young, and it can wait

Millions of Americans may be using this convenient excuse, especially if they're still in their 20s. That's a crying shame, though, because the younger you are, the more powerfully you can amass wealth, which might even permit you to retire early. Check out the table below, which shows what you could accomplish:

Growing at 8% for

$5,000 invested annually

$10,000 invested annually

$15,000 invested annually

5 years

$31,680

$63,359

$95,039

10 years

$78,227

$156,455

$234,682

15 years

$146,621

$293,243

$439,864

20 years

$247,115

$494,229

$741,344

25 years

$394,772

$789,544

$1,184,316

30 years

$611,729

$1,223,459

$1,835,188

35 years

$930,511

$1,861,021

$2,791,532

40 years

$1,398,905

$2,797,810

$4,196,716

Source: Calculations by author. 

If you're 25 now, for example, you might have $1.4 million by age 65, by only investing $5,000 annually, which amounts to about $420 per month. (Of course, as you get older, you'll likely be able to sock away much bigger sums annually, meaning you'll end up with much more money, or you might be able to stop working earlier.) Even if you're 35 now, by socking away $15,000 annually (equal to $1,250 per month) for 25 years, you could end up with more than a million dollars by retirement -- at age 60! The earlier you start, the more possibilities you have.

Excuse No. 2: I'm too old at this point

Just as it's rarely too soon to start investing for your future, it's also rarely too late. Even if you only have a few years before you hope to retire, if you can save aggressively, perhaps by spending less and making money on the side, you can make your retirement a little or a lot more comfortable. If, by doing so, you amass an extra $120,000, that can provide an extra $12,000 annually ($1,000 per month) for a decade or so, and possibly longer. The table below offers some specific examples.

Growing at 8% for

$10,000 invested annually

$15,000 invested annually

$20,000 invested annually

3 years

$35,061

$52,592

$70,122

4 years

$48,666

$72,999

$97,332

5 years

$63,359

$95,039

$126,719

6 years

$79,228

$118,842

$158,456

7 years

$96,366

$144,549

$192,733

8 years

$114,876

$172,313

$229,751

9 years

$134,866

$202,298

$269,731

10 years

$156,455

$234,682

$312,910

Source: Calculations by author.

A young man is smiling in front of a blackboard with financial images on it.

Image source: Getty Images.

Excuse No. 3: I don't know enough

It's easy for most of us to assume that we don't know enough to be investing in the stock market (or in bonds or real estate or other investments). After all, few of us are ever taught much about managing and growing money, and money is a bit of a taboo topic in society, as well.

Fortunately, investing isn't rocket science. Take it from super investor Warren Buffett. Here's what he reportedly said in an interview in India:

The good news I can tell you is that to be a great investor you don't have to have a terrific IQ. If you've got 160 IQ, sell 30 points to somebody else because you won't need it in investing. What you do need is the right temperament. You need to be able to detach yourself from the views of others or the opinions of others.

You do need discipline, determination, and the ability to do a little math, and you can learn enough to get started with just a book or a few books.

Excuse No. 4: I don't have time

Of course, you might not want to dive into learning all about investing, perhaps because you just don't have the interest in it, or maybe because you don't have the time. Fortunately, all is not lost. There's an excellent option available to you: Index funds.

A low-fee, broad-market index fund is a mutual fund that tracks a particular index, such as the S&P 500 (which is made up of 500 large American companies). Index funds tend to sport much lower fees than other mutual funds, where highly paid managers have to study investments and decide when to invest in what. Index funds simply have to own whatever is in the index they're tracking, so they require much less brainpower and labor.

Some good index funds to consider are the SPDR S&P 500 ETF (SPY), Vanguard Total Stock Market ETF (VTI), and Vanguard Total World Stock ETF (VT), which will, respectively, spread your dollars across 80% of the U.S. market, all of the U.S. market, or most of the world's stock market. There are index funds that track bonds and other segments of the market, too.

Excuse No. 5: I don't know where to start

You might start by spending more time at Fool.com where we offer much guidance on how to invest -- in stocks, bonds, real estate, and other things. You can also find a host of Motley Fool books at your favorite local bookstore or through many online retailers.

In addition, consider checking out John Bogle's The Little Book of Common Sense Investing, Peter Lynch's classic One Up on Wall Street, and Joel Greenblatt's The Little Book That Still Beats the Market. Books about great investors, such as Roger Lowenstein's Buffett: The Making of an American Capitalist, also provide great insight into investing. And if you want to just stick with index funds, you can learn a lot about them in articles at Fool.com.

Don't let yourself avoid or put off investing due to excuses. The reward -- increased financial security -- is too great to ignore, and the risks too great to bear.

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.