Helaine Olen and Harold Pollack are the co-authors of the new book "The Index Card: Why Personal Finance Doesn't Have to be Complicated," which offers 10 rules that regular people can follow to manage their own money, without getting a degree in finance or paying high fees.

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What you need to know is so straightforward, they argue, that it can be written down on a single card and posted on your fridge. We sat down with Olen to talk about what those simple money principles are, and why they remain so elusive for most of us.

Is paying professionals to manage portfolios worth it?

We are all pitched the idea that managing money is really hard, and that professionals have some special secret that can help you. In fact, most of this stuff is pretty basic, and can be put on a single index card. I get that people are legitimately busy, and that money management is a task they find unpleasant. So it tends to be put off, or given to someone else like a financial adviser. Since they are the experts, they should know what they are doing, right? But the majority of advisers aren't even legally bound to act in the best interests of their clients. People don't even realize that.

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When Harold Pollack's finance plan index card went viral, did you realize how much of an effect it would have?

The exact opposite, actually. We had talked about it in an interview, but then without thinking much about it, he took an index card from his daughter's knapsack, scrawled some thoughts on it with a Sharpie, and put a picture of it online. Then it just took off. I guess it distilled a lot of things that people knew into a simple, easy-to-understand format.

So what are a few of these simple tips?

Save 10-20 percent of your money. Pay down credit-card debt, ideally the full amount every month. Max out your retirement accounts, at least up to the amount of the employer match. Don't invest in individual stocks. Use broad, low-fee index funds instead. Make sure you are properly insured. Only buy a home when you are financially ready, not because you think you have to.

You have been pretty outspoken that the 401(k) system is not working, and that the system is stacked against most of us. How does that jibe with your book, which suggests people can take control of their future?

It is true that I don't think that the 401(k) system works for everyone. On the other hand, it is a fact that we all live within it. I can't get up on my high horse and say we should all boycott 401(k)s. I use mine, and you should use yours, if you have one. But of course I would like to see the system improved. It is what we have, and we all have to learn how to best take advantage of it. The more attention people pay to investment fees, for instance, the lower they will go.

Since these money precepts are so simple, where do most people go off-track?

They go off-track in terms of not saving enough. Half of Americans are living paycheck-to-paycheck, and don't have any emergency savings at all. The second place where they go off-track is that they think their financial adviser is their pal, and is always doing what is in their best interest. That is not always true.