You'd love to have a comfortable retirement. But who wants to spend the best years of their lives thinking about getting old?

That's probably the biggest challenge that many investors face in trying to save for long-term goals, whether you're saving for a down payment on a home, trying to put your kids through college, or accumulating enough money to live the rest of your life after you quit your jobs. In contrast to the immediate payoff that so many things you do give you, long-term saving is slow, tedious -- and lately, it hasn't been very rewarding.

But face it: As much as you want the good life now, you also want the happiness that money will bring you in the future. So with that in mind, consider four of the most common mistakes investors make in trying to save for a long-term goal.

1. Being late to the game
When you don't really want to do something, it's easy to put it off. But in investing, delays can be extremely costly. That's a lesson that may seem counterintuitive lately -- after all, if you've procrastinated investing money since 2007, you may feel like the smartest person alive. But in general, the sooner you start saving, the more you'll accumulate during your lifetime.

For instance, consider two couples who are nearing retirement now. One couple started saving 30 years ago and has kept adding money throughout their careers. The other couple kept putting off saving until just 15 years ago, when they turned 50 and realized they were running out of time.

At first glance, you might think that the first couple might be twice as well off as the second, since they've had twice as long to invest. Yet money put in 30 years ago has a much bigger advantage over money put in 15 years ago. Take a look at some examples from among Dow 30 stocks, the cream of the crop that many investors turn to for a buy-and-hold strategy:

Stock

15-Year
Total Return

30-Year
Total Return

United Technologies (NYSE:UTX)

543%

4,137%

Boeing (NYSE:BA)

76%

1,488%

3M (NYSE:MMM)

164%

1,710%

IBM (NYSE:IBM)

677%

932%

Procter & Gamble (NYSE:PG)

362%

4,393%

Source: Yahoo! Finance.

Notice how the difference isn't two times -- it's more like 10 times in many cases. And although the overall stock market did better from 1979 to 1994 than from 1994 to 2009, that's exactly the point: You don't know when stocks will do best, so you need to be invested as long as possible to take advantage of the good times when they do come.

2. Not taking risk
Even those who get on the saving bandwagon often think it's good enough to put their money in relatively safe investments. Unfortunately, that squanders much of the advantage of starting early -- the power of compounding doesn't work too well on a short- or medium-term Treasury note yielding 3% or less. It may be tough for new investors to invest in seemingly risky stocks such as Blackboard (NASDAQ:BBBB) or Chipotle Mexican Grill (NYSE:CMG), but it's small companies like these that tend to perform best over the long haul.

3. Missing out on smart tools
Investors have big advantages in saving for long-term goals. For retirement, IRAs and 401(k)s can help you reap huge tax benefits. Similarly, for college savings, 529 plans give you valuable tax deferral. If you don't use the tools you've been given, you're missing out -- and it'll take you much longer to get to the finish line.

4. Not knowing the true cost of your goals
Sure, it's easy to say you need $1 million to retire well. But how do you really know? If you don't take the time to figure out exactly what you want to do in your golden years, you really have no idea -- and could easily take the wrong path to get there. There's nothing sadder than seeing someone save and save trying to reach some arbitrary net worth -- only to get there and find out that they could have retired years ago.

As hard as it may be to believe right now, you can reach your long-term financial goals. But you can't afford to make mistakes. If you're not doing everything you can to succeed, take a close look at yourself and figure out how to do more. Your future self will thank you.

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Fool contributor Dan Caplinger still makes plenty of mistakes. He doesn't own shares of the companies mentioned in this article. Chipotle Mexican Grill 'B' shares and Blackboard are Motley Fool Hidden Gems selections. 3M is a Motley Fool Inside Value pick. Chipotle is also a Motley Fool Rule Breakers recommendation. The Fool owns 'B' shares of Chipotle. Try any of our Foolish newsletters today, free for 30 days. The Fool's disclosure policy won't let you make a mistake.