Reproof is a medicine like mercury or opium; if it be improperly administered, it will do harm instead of good.

Correction is a strong medicine, and the dose and the timing matter more than the accuracy. The same true observation delivered in front of others, or when someone is already at the end of their reserves, does damage the content cannot undo. Being right about the substance does not make the delivery harmless. A great deal of well-intentioned criticism lands as an injury and is remembered as one for years.

Before offering a correction, decide on the moment and the audience deliberately. Privately, once, when the person has the capacity to hear it. Say only the part they can act on, which is usually much smaller than what you noticed.