The proverb is not about being nice. Gentle here is closer to soft or tender, and it describes the answer rather than the person giving it. You can be entirely right and still choose how the sentence lands.
Picture a kitchen at eleven at night. Someone comes in from a long shift, sees the dishes still in the sink, and says something sharp about it. You washed half of them. You have a reply ready, and every word of it is accurate.
Notice it says turns away. The wrath is already there. Somebody has arrived angry and the proverb assumes you did not cause it. Your job is not to win the exchange, it is to change its direction.
The second half is the warning. A harsh word stirs up anger, and stirring is what you do to something that had settled. The harsh word does not merely fail to help. It reaches into a situation that was calming down and brings it back to a boil.
This saying sits in a long run of two line proverbs, most of them built the same way. One line shows the wise path, the next shows the foolish one, and the reader is left to notice the gap between them. Chapter 15 comes back to speech again and again. The tongue, the lips, the mouth. The book treats words as things that do something to people, not only things that mean something.
Most arguments have one moment where both replies are available. You can feel it happen. There is a sentence ready to go and a quieter one waiting behind it. The first one usually feels like honesty. It is often just speed.
Pick the quieter one today, once, on purpose. When the moment comes, lower your voice a notch, answer the thing that was actually said rather than the tone it was said in, and leave the correction until tomorrow. If it still needs saying then, it will keep.
