Notice the Buddha isn't claiming he discovered anything here, he calls it an old rule, the kind everyone already knows and nobody quite manages to use the next time someone cuts them off in traffic or fires back a sharp reply. Matching heat with heat feels like justice in the moment, but it just adds a second fire where there was one. Today, when someone's tone lands wrong, in an email, on a call, in the kitchen, try meeting it with something other than more of the same, and watch the temperature in the room.
For hatred does not cease by hatred at any time: hatred ceases by love, this is an old rule.
The Dhammapada, verse 5 (trans. F. Max Muller)