A more thorough explanation:

The error-of-judgment rule is a doctrine that protects professionals from liability for advice or opinions given in good faith and with an honest belief that the advice was in the client's best interests, but that was based on a mistake either in judgment or in analyzing an unsettled area of the professional's business.

For example, an attorney who makes an error in trial tactics involving an unsettled area of the law may, under certain circumstances, defeat a malpractice claim arising from the tactical error. This means that if the attorney acted in good faith and believed that their tactics were in the best interest of their client, they may not be held liable for any negative outcome resulting from the error.

The error-of-judgment rule is important because it allows professionals to make decisions based on their expertise and experience without fear of being sued for every mistake they make. However, it is not a blanket protection and only applies in certain circumstances where the professional acted in good faith and with an honest belief that their actions were in the best interest of their client.