Investor psychology is the most important event that guide the market. In this sense, news and developments are always used to conduct perception operations on the investor.
Investor need to have the best of the logic and rationale behind their buy/sell. They cannot act silly like the panic sellers who just fear on everything and do not believe in what they buy and sell it as soon as market even drops a bit and create more havoc in the market. Some times news by media are also interpreted as wrong and results in the dip in the market.