Most people know the rule is to buy low, sell high. If you buy that, the problem is knowing when the market has peaked or bottomed out. A growing number of Thrift Savings Plan investors are nervously wondering how much longer the current bull market — 10-plus years without a correction of 20% or more — will last, and can last. So many things could go wrong: Turkey and Syria, Chinese trade and the Hong Kong problem, post-Brexit Europe, or impeachment — a major disaster. Arthur Stein, a Washington, D.C.-area certified financial planner, weighs in on this episode of Your Turn with Mike Causey.