I've always loved those charts that investment companies and advisors put out, while they really drive home the importance of compound interest, they always paint a picture through rose colored glasses that leaves out all the bumps and opportunities along the way. Nobody has to look to far past the last 20 to 30 years to see how erratic the markets have been including the "Lost Decade" in the mid to early 2000's where there was little to no growth. While these charts paint a nice picture of what "Could happen" if one invested early for 10 years, it doesn't take into account the large swings in the markets and the value of dollar cost averaging. In the real world investing over the long term will have advantages not shown in these charts. While I strongly agree that they start as soon as possible like the chart suggests, the greater value will come with investing over the long term. If a person invest the same amount each month over the long term they will be able to take advantage on times when the markets are way down, their investment amount will buy more shares during the down times and grow faster in value as the markets rise giving them more in returns. The person that invests for only 10 years and stops will simply ride the ups and downs without getting any of the benefits.
I apologize, I in no way meant to downplay the importance of starting to invest early and agree with all everyone has said here, it's just that these charts can be so deceiving to young investors that think they can just stop investing after a few years and come out way ahead of others that stay the course.
I did have to chuckle though. 12% annual return for every year, that's just not fair it's a fairy tale.