"Rumors," Claude said over the phone, not with annoyance or complaint but with admiration, "Eisner really is an old fox. Such a simple little trick, yet it made us suffer a significant loss."
Rumors are the simplest and most common tactic in finance. To exaggerate a bit, the randomness of finance is only a bit higher than that of quantum states. Speaking of stocks, perhaps one second they are surging dramatically, but the next they could be plummeting. Even Buffett wouldn't dare guarantee he could catch those fleeting opportunities every time, let alone anyone else.
It is because of this characteristic that financial matters are easily influenced by external factors, and rumors are the easiest way to have an effect. If there are talks that a company's executives have met with bankers, that a major investor is planning to pull out of a company, internal discord within a company, etc., such news will certainly cause the company's stock to fluctuate.