Assets tend to correlate in volatile markets. There are plenty of papers discussing this effect. Because of diversification, people often need to sell higher pe

Assets tend to correlate in volatile markets. There are plenty of papers discussing this effect. Because of diversification, people often need to sell higher performing assets to cover lowering performing ones. A friend ran a successful small investment fund, and still went out of business during the last down turn because all his clients had to pull their money out to cover losses elsewhere.