Financial advisors who beat the save-early-and-often drum might want to stifle their agonized groans. To that point, 59 percent of investors ages 18 to 34 say they already have taken money from their retirement account, according to recent research by E-Trade Financial. That figure has been growing steadily since 2015, when it was 31 percent. "There's a temptation to access retirement accounts, but it should be an option of last resort," said Mike Loewengart, vice president of investment strategy at E-Trade.

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Despite the prevalence of these early withdrawals, most younger investors (89 percent) are either somewhat or very confident that they will save enough to enjoy their retirement, the research shows. They also should make sure they fully understand the impact of tapping retirement savings before age 59½. Early withdrawals from 401(k) plan accounts and IRAs — excluding Roth versions of both — are subject not only to regular income taxes, but also a 10 percent early withdrawal penalty unless you meet one of a few exclusions. On top of the potential tax cost, you're removing money intended to stay put so it can grow over several decades, experts say. In other words, when you withdraw, for example, $10,000, you're taking out more than that amount — you also are eliminating all the potential earnings and interest it would earn over several decades.

Those compounding gains are nothing to sneeze at. For illustration purposes: $10,000 invested in the S&P 500 index in January 1988 would have grown to $211,900 by the end of 2017, according to MoneyChimp's online calculator. Despite the consequences, many people who find themselves in a financial pinch turn to their retirement savings. The top reason cited for the withdrawal was medical emergencies (23 percent), followed by education expenses (22 percent) and unemployment (17 percent).