Few investors, if any, sail through life without making mistakes, but when it comes to retirement investing, serious missteps can cost you. For instance, unadvertised fees are easy to discount, but investors do so at their peril. Paying an extra 1 percent in fees every year over the span of a career can leave your account lighter by tens of thousands of dollars at retirement, according to the Department of Labor.

Similarly, ignoring unseen sources of risk can also prove detrimental. Since the market crash in 2008, many investors have been wary of taking aggressive risks with their portfolio for fear of losing money. But investing too conservatively can pose even more risk in the long run.

Unfortunately, workers are largely on their own when it comes to funding their retirement, and that necessitates learning everything possible about the best way to get there — especially how to avoid the biggest retirement investing mistakes.