People are likely to obey the commands of those in authority. Usually, this serves a useful purpose, as the one in power is often an expert in the relevant subject. The alternative to a society in which a chain of authority exists is one of anarchy, which is not nearly as productive. However, when those in authority make mistakes, this tendency to listen to them without thinking can lead to disastrous consequences.
In the famous Milgram experiments, subjects were willing to put other subjects through intense (fake) pain, simply because an authority figure was telling them it was okay. Many of the atrocities committed during World War II are attributed to this phenomenon.
This tendency to stop thinking because the authority figure must be right can also be taken advantage of by those in the know. Con artists will often pretend to be authority figures (e.g. policemen, bank officers) in defrauding their victims. "Experts" in the stock market will tell you to buy their services. Marketers will use paid actors dressed as doctors to tell you to use a product.
Even if viewers know its an actor playing a doctor, they are still more likely to buy the product being offered than if the actor is playing a layman, which is baffling! A person's title, clothes and trappings (e.g. the type of car they drive) have all shown to be significant determinants of whether people are likely to follow their instruction, often subconsciously!
Investors must be sure to think for themselves, and not purchase stocks or services simply because a perceived authority figure is claiming it's the right thing to do.