The phrase was made famous by Nietzsche and has older Stoic roots in Epictetus and Marcus Aurelius.
How to Practice
Choose one thing from today that you wish had gone differently.
Keep the scope small and specific. Pick the cancelled plan, the careless comment, the mistake, or the delay, rather than trying to take on your whole life at once.
Write the bare facts in two or three sentences.
Describe what happened as a camera might record it, without motives, predictions, or verdicts. For example, note that an email received no reply, then leave aside the story that you are being ignored forever.
Name what you wanted instead.
Say plainly what you had hoped for: respect, ease, more time, a different outcome. This makes the resistance visible, which is more honest than pretending the event did not matter.
Let the fact be true for one minute.
Sit still, breathe normally, and repeat the facts silently. You are not required to enjoy them; you are practicing the harder move of no longer arguing with what has already occurred.
Say yes to its place in your life, with a clear boundary around harm.
Try a simple sentence such as: This happened, and it belongs to the life I have to meet today. This never means approving of harm someone did to you, excusing them, or staying in an unsafe situation.
Ask what the situation asks of you now.
Choose one response within reach: send a direct message, apologize, rest, document what happened, ask for help, or make a plan for tomorrow. The Stoic thread in this practice is to give your attention to your own judgment and action.
Close by carrying one useful detail forward.
Write one line about what this event has shown you, such as a limit you need, a conversation to have, or an expectation to loosen. Return to the note tonight if the same thoughts keep pulling you back into the event.