This article is by Eric Oberg, who worked in fixed income, currencies and commodities for Goldman Sachs for 17 years before retiring as a managing director. To join a discussion about short ETFs, please visit our special forum on Stockpickr.com.What would you say if you bought an index fund, only to find out that it lagged the benchmark by 30%? 80%? Over 100%? I am sure you'd be dismayed, disappointed and disgruntled.