Most Americans take for granted that their financial advisor will represent their best interests, but this is less true than you might think. In fact, up until recently, the people we trust with our money have been free to accept kickbacks for steering clients into retirement plans based on what's most profitable for the broker, not necessarily the investor.
That changed with a rule passed by the Obama administration. Set to take effect in April, it's called the fiduciary duty rule, and it looks like the Trump administration is gearing up to do away with it.
A fiduciary duty is the "highest standard of care" the law requires. Also applied in fields such as law and business, it requires practitioners to serve the best interests of their client above all others. Professions generally apply this standard to jobs that meet two criteria: first, a high degree of specialty and knowledge, such that the layperson cannot necessarily understand or competently overrule the advice being given. Second, the ability to do great harm through self-interest.
These criteria broadly establish the two most common elements of a fiduciary duty: the duty of care and the duty of loyalty.
In many circumstances, the need for this rule is obvious. Otherwise a lawyer could sell out his client in exchange for political favors, or an executive could tank the company's stock price to get a plum job with a rival corporation. By contrast, despite the specialized nature of his job, the average mechanic is not held to a fiduciary duty because the scope of harm is minor relative to the damage one could do with power of attorney.