If you're within a decade of retirement, the current stock market volatility may be a good reminder of a key risk that lies ahead for your nest egg. While stocks tend to offer the best opportunity for long-term growth despite their ups and downs, a persisting market downturn heading into retirement can be problematic if you'll need to tap those assets when prices are down. That can permanently reduce how long your portfolio will last, said certified financial planner Mike Casey, founder and