Commentary on Meditations: B1.10

10. From Alexander the grammarian: not to leap on mistakes, or captiously interrupt when anyone makes an error of vocabulary, syntax, or pronunciation, but neatly to introduce the correct form of that particular expression by way of answer, confirmation, or discussion of the matter itself rather than its phrasing - or by some other such felicitous prompting.

In this passage, the main quality which Marcus admires is the quality of giving good feedback and coaching well. Giving feedback in order for it to be effective means providing it with tact. Tact entails being sensitive in dealing with others or with difficult issues. If someone makes a mistake, then don't be that "know-it-all" and immediately jump all over the person. Rather, start with what they did well and then offer ways for them to improve.

Think of Hermione and how she somewhat arrogantly corrects Ron: https://www.youtube.com/watch?v=fx2zLgdkJpk