yeah there are some market forces that is controlling the market because when a large trader gets into the market you would see that the market won't be stable or possibly if there were sad news about the market you would notice the changes in market, but most times there are people who may decide to hold and not to trade because market may easily recover after some while or when the news is notice to fiction or not authenticated.
There are different factors that play a role in market fluctuations and most of the time the effects of news are very strong which can suddenly alter the market price. Selling and buying in large percentage can also influence the market price but this cannot be done by common investors who just invest in a single coin but those who invest largely in every successful coin can influence the worth of the market.
For managing the situations we cannot sell our coins when there happens a decrease in the value but we can hold it to avoid failure because without holding we cannot reach our destination.