Personal finance is full of simple rules — guideposts to decisionmaking. Here's one: How much can you withdraw from your retirement portfolio annually without worrying (too much) about running out of money? The 4% rule says plan on withdrawing that much every year, plus the rate of inflation.

Rules like these if followed mindlessly could be bad for your financial health. But guidelines exist for good reasons. You have to start somewhere.

The latest controversy about rules involves the so-called 60/40 portfolio. This guidepost suggests constructing a long-term portfolio for all seasons by putting 60% in a broad-based equity index fund (such as the S&P 500) and 40% into fixed-income securities (usually a mix of U.S. Treasury securities or a high-quality bond index fund). The portfolio mix has worked well for decades, but the core argument against it is that the "40%" part of the portfolio will deeply disappoint in generating income in coming years with low interest rates. A recent Bloomberg story reports that two sovereign wealth funds say "investors should expect much lower returns going forward in part because the typical balanced portfolio of 60/40 stocks and bonds no longer works as well in the current rate environment."

Much of the debate seems like something of a sham for individual investors. For one thing, the 60/40 portfolio is a starting place for thinking through the asset mix for your particular circumstances. The actual answer lies with a combination of factors, such as your age and your household financial capacity for risk. More importantly, warning bells go off with many of the proposed alternative investments that are typically more complicated, involve taking on greater risk and come with higher fees.

Interest rates are also likely to rise as the economy strengthens. When yields rise, bond prices fall. Since most long-term individual investors own fixed income securities in mutual funds, they will get to reinvest their money into higher yielding bonds which, with time, should generate more interest income. The real issue for those dependent on portfolio income (such as retirees) is to have enough set aside in cash to meet expenses during periods of market turbulence.

The 60/40 portfolio strategy may do well or less well in coming years. Like the 4% rule and similar guideposts, the value is that it is a time-tested heuristic. Then the real work begins.

Chris Farrell is senior economics contributor, "Marketplace" commentator, Minnesota Public Radio.