The general rule of the thumb is you do not make any loss until you sell your assets. Let's say you bought stocks when the price was $10, and now the price is $5. If you avoid selling below the price point of $10, you will never make any losses even when the market is down. If you wait until the price goes up, you will never make loss. Sadly, not every one can do this as people might need to pull out as they might need money. If you do not have the capacity to hold your assets while the market is down you might make losses. Therefore in order to avoid making losses you need to make sure you can hold your investment for a long time.