Even the most basic financial plan calls upon you to make your best guess about a few key facts: how much you can kick in on an ongoing basis; how much time you have to invest; what combination of stocks and bonds you employ; and finally, the rate of return you can expect to earn on your investments.
The first three fall into the realm of "somewhat knowable," and you exert at least some control over them. But forecasting returns is a trickier business.
Christine Benz does not own shares in any of the securities mentioned above. Find out about Morningstar's editorial policies.