Some researchers call the years immediately before and after retirement “the fragile decade,” because investment returns during this period take on outsize importance. This is partly because of so-called sequence risk. That’s the chance that you will be withdrawing money from your investments at exactly the wrong time, when values are low. Those assets will never have a chance to rebound as you age.

The financial planner Ann Minnium encourages more conservative investing during the fragile decade and finds that clients often push back, wanting bigger returns. “I let them know that five to 10 years into retirement, they can increase their exposure to equities if the plan is on track and they are still interested in taking additional risk,” said Ms. Minnium, who is based in Scotch Plains, N.J. “Sometimes knowing that they may only need to play it safe temporarily is enough to get them to implement the more conservative portfolio, which will ultimately improve their retirement plan success.”

Your real appetite for risk: What is it?

The truth is, many people think they are more comfortable taking risk than they really are. Then the market swoons, and they panic. Planners often use online tools such as FinaMetrica, Riskalyze and Tolerisk to help gauge the amount of risk their clients are actually comfortable taking.

Clients answer several questions about money; for example, “If you had to choose between more job security with a small pay increase and less job security with a big pay increase, which would you pick?” In the end they get a score that reflects their risk tolerance and, in some cases, their capacity for risk. A bigger portfolio or lower expenses, or both, will increase your risk capacity.

Ben Rickey, an adviser in Yakima, Wash., is a fan of Riskalyze. “It’s very relatable. They have a graphic that looks like a speed-limit sign,” he said. “So the Standard & Poor’s 500 stock index has a speed limit right now of around 74,” he might say to a client. “What’s your speed limit?”

Once he knows a client’s risk tolerance score, Mr. Rickey creates a model investment portfolio based on it, along with some more aggressive portfolios. Then he compares them, using software that calculates the odds of any portfolio lasting the rest of a person’s life. “A lot of times they’ll find that by taking more risk they actually increase their chance of running out of money before they die, because it increases the variability so much,” he said.

Mr. Fonville likes to show his clients a chart with the returns for two portfolios: one with 100 percent large stocks, and the other a diversified mix of stocks and bonds. “Which one would you prefer?” he’ll ask. They will always say the one with 100 percent stocks because it produces larger returns.