Experts in the stock market, real and self-anointed, know that historically it has gone up and down due to a variety of things — some predictable, some coming from out of left field. Buying stocks during the Great Depression was, in hindsight, a smart move. Shares were on sale but most people didn’t get it, or couldn’t afford it in the 1930s when they were too busy trying to find work, food and pay the rent. Some TSP investors see the current crisis as a buying opportunity. They are assuming that shares in the stock-indexed C, S and I funds are on sale and that, like during the Great Recession of 2008-2009, this too shall pass. Others are not so sure. Fans of the treasury securities G fund believe recent events have proven that while its yield is low, it never has a loss. So we asked Washington, D.C.-area financial planner Arthur Stein for his take. He knows the TSP well after working with the House Ways and Means Committee and after years as a professor and financial adviser.