अनुद्वेगकरं वाक्यं सत्यं प्रियहितं च यत्।स्वाध्यायाभ्यसनं चैव वाङ्मयं तप उच्यते॥
anudvega-karaṃ vākyaṃ satyaṃ priya-hitaṃ ca yatsvādhyāyābhyasanaṃ caiva vāṅ-mayaṃ tapa ucyate
Word by word
The verse says
Words that do not wound, that are true, that are kind and that do some good; and keeping up your own reading. This is called the discipline of speech.
In plain words
Four conditions on a sentence before you say it. True, kind, useful, and not causing distress.
Most of what gets said fails at least one. That is not a scolding - it is arithmetic.
And notice that truth alone does not get you through. A true sentence that only wounds fails three of the four. Honesty is not allowed to be used as cover.
Where you've felt this · in friendship
Your friend asks what you think of the thing he has spent a year on. You can see three problems with it. You name the one he can actually fix, you tell him what is good, and you do not mention the other two that afternoon. Nothing you said was false. You simply did not use everything you had, and he went home able to work.
Going deeper
Truth being necessary and not enough on its own is the whole content of this verse, and it is the most practical thing in the chapter.
Four conditions are stacked: not wounding, true, agreeable, and doing some good. All four together. Drop any one and you get a familiar kind of person. True but wounding is the man who is honest at your expense. Agreeable but untrue is flattery. Kind and true and useless is noise.
The hardest is the first, because it rules out the move most of us make when we are hurt - telling the exact truth, sharp end forward, and then standing behind the fact that it was true.
And the last item is strange company for the others: keep up your own reading. It is there because speech comes out of what has been going in. A person who has read nothing for a year will eventually run out of things worth hearing.