An important principle at the heart of the Efficient Market Hypothesis is the law of one price. The law asserts that in an efficient market, the same asset cannot simultaneously sell for two different prices. If that happened, there would be an immediate arbitrage opportunity, meaning a way to make a series of trades that are guaranteed to generate a profit at no risk.
News and Noises
The only thing that makes an investor change his mind about an investment is genuine news.
But humans might react to something that does not qualify as news, such as seeing an ad for the company behind the investment that makes them laugh. In other words, there are many who make decisions based on noises rather than actual news. These are called "noise traders". They trade on noise as if it were information. "THERE ARE IDIOTS. Look around."