One great benefit of a financial plan is that it gives you a feeling of certainty. Designed to take into account wide-ranging scenarios, it seemingly should be able to shrug off an uptick in inflation, a bear-market stretch for stocks, or a spike in interest rates. Yet there are some circumstances—such as the recent once-in-several-decades plunge of the economy and financial markets—that even the most carefully constructed plan can’t fully anticipate. Such events, as well as possible changes in your own situation, mean that every financial plan, sooner or later, will have to be revised. Preparing a financial plan is a process, not a one-time event, and making smart, timely alterations is crucial.

Consider how that process works. A financial advisor takes stock of an investor’s overall financial situation and asks questions about goals, comfort level with investment risks, and the timetable for using investment proceeds. Then, the advisor establishes a comprehensive plan designed to help achieve those objectives.

That requires several assumptions about how markets and the economy will behave. For example, an advisor might base a plan on a projected inflation rate of 3%, an 8% average annual return for stocks, and 4% yearly gains for bonds. Though some or all of those assumptions might miss the mark, the idea is that, taken together, they should be close enough to be useful. Yet even small inaccuracies, left uncorrected for 20 or 30 years, will leave a plan seriously out of whack.

Think of a ship setting out from New York for, say, Lisbon. The captain charts a course that should take the ship across the Atlantic to Portugal. But what if he makes a small miscalculation? Even if he’s off only 1%, that could be a problem, and unexpected changes in winds and currents along the way are likely to make things worse. If he sticks to his original bearings, he could end up in Africa—or Ireland.

But that won’t happen, because every good sailor understands the need for minor but constant course corrections. And a financial plan requires similar adjustments. Look at the predictions of economists, market forecasters, or the government, and you’ll see that no estimate extending more than a year or two into the future will be even close. So a financial plan written to predict the feasibility of a retirement 30 years away won’t—and can’t—be accurate. But it can establish a starting point. Reaching your goals requires frequent adjustments to compensate for the winds and currents you meet along the way.

Once you understand that basic certainty, you can prepare by discussing how, and under what circumstances, your plan will need to be altered. We would be happy to review your plan with you to make sure it continues to move you toward your long-term goals.