Although it has become much easier for individual investors to adjust their retirement accounts as often as they wish, human nature is such that most people are still inclined toward just leaving their allocations be, even if they know it's probably not in their best interest to do so.

In fact, many people don't even adjust their portfolios on an annual basis, says Victor Ricciardi, a professor of finance at Goucher College in Baltimore, Md., despite the fact that an increasing number of companies allow investors to automatically set up an annual rebalancing online.

Ricciardi—who has done extensive research in the fields of behavioral finance and the psychology of risk—attributes this lack of proactive investment behavior to what he calls "the anchoring effect." The anchoring effect causes individuals to cling to a belief that may or may not be true, and to base their decisions for the future on that belief. The inertia and inattention that this leads to can have detrimental effects on their retirement accounts.