Terms that are often used, often lose their meaning.  What is legal malpractice?  It’s a situation in which  an attorney is retained to represent a client, takes on the case, departs from the standard of good practice for an attorney in similar representations, and where that departure from good practice proximately leads to a bad economic result, but for which departure from good practice there would have been a better economic result for the client.

That’s more exact than “the attorney made a mistake.”

Similarly, in a breach of fiduciary duty, what exactly is that fiduciary duty?  Here, we have Deutsche Bank Natl. Trust Co. v Sidden , 2017 NY Slip Op 27074, Decided on February 24, 2017, Supreme Court, Queens County where Judge Modica channels Judge Cardozo:

“In a beautifully written and scholarly article, “Understanding Fiduciary Duty,” (Fla. B.J., March 2010, at 20, 22), Florida lawyers John F. Mariani, Christopher W. Kammerer, and Nancy Guffey-Landers, Esqs., discuss the fiduciary duty:

The most basic duty of a fiduciary is the duty of loyalty, which obligates the fiduciary to put the interests of the beneficiary first, ahead of the fiduciary’s self interest, and to refrain from exploiting the relationship for the fiduciary’s personal benefit. This gives rise to more specific duties, such as the prohibition against self-dealing, conflicts of interest, and the duty to disclose material facts. Perhaps [*3]the most famous description of the duty of loyalty is by Chief Judge Benjamin Cardozo in Meinhard v. Salmon, 249 NY 458, 464, 164 N.E. 545, 546 (1928):

Many forms of conduct permissible in a workaday world for those acting at arm’s length, are forbidden to those bound by fiduciary ties. A trustee is held to something stricter than the morals of the market place. Not honesty alone, but the punctilio of an honor the most sensitive, is then the standard of behavior.

In addition to a duty of loyalty, a fiduciary also owes a duty of care to carry out its responsibilities in an informed and considered manner and to act as an ordinary prudent person would act in the management of his or her own affairs. If the fiduciary has special skills, or becomes a fiduciary on the basis of representations of special skills or expertise, the fiduciary is under a duty to use those skills.

John F. Mariani, Christopher W. Kammerer, Nancy Guffey-Landers, “Understanding Fiduciary Duty,” Fla. B.J., March 2010, at 20, 22 (footnote references omitted).

Aside from Cardozo’s famous statement in Meinhard, made in 1928, for the New York Court of Appeals, the Supreme Court of Florida, one year earlier, in Quinn v. Phipps, 93 Fla. 805, 113 So. 419 (1927), articulated, with equal polish:

Stripped of all embellishing verbiage, it may be confidently asserted that every instance in which a confidential or fiduciary relation in fact is shown to exist will be interpreted as such. The relation and duties involved need not be legal; they may be moral, social, domestic or personal. If a relation of trust and confidence exists between the parties (that is to say, where confidence is reposed by one party and a trust accepted by the other, or where confidence has been acquired and abused), that is sufficient as a predicate for relief. The origin of the confidence is immaterial.
Quinn v. Phipps, 93 Fla. at 811, 113 So. at 421 (1927).”