If markets drop enough the losses could trigger a negative feedback loop where financial institutions automatically begin liquidating positions in order to obtain the liquid assets to cover their debts in case investors see the losses and decide to withdraw in a panic. This floods the market, driving prices down further, and potentially triggering even more automatic liquidation, leading into a death spiral.<p>Conversely, there is no mechanism that can push the market increasingly higher, other than hyperinflation or a collapse in, say, the bond market which might theoretically drive investors into equities. But if the bond market collapses, the world has much bigger fish to fry and the stock market will probably come down right afterwards.