Accept reality
Principle 8 from the Enchiridion
Acceptance gives us somewhere honest to begin. We waste less energy when we stop demanding that reality match the plan in our head.
Original Passage
Don't demand that things happen as you wish, but wish that they happen as they do happen, and you will go on well.
Modern Interpretation
The idea is clear, even if it is hard to live: stop demanding that reality follow your script. A lot of frustration lingers because we keep arguing with something that has already happened.
Acceptance does not mean approval, and it does not mean doing nothing. It means starting with the facts you have rather than the version you wish had happened. From there, you can choose what to do next.
The energy spent repeating, "This was not supposed to happen," becomes available for dealing with what is actually in front of you.
In Practice
You planned an important day, and someone cancels at the last minute. Being annoyed is understandable. But once it happens, the new situation is the one you have to work with.
Ask, "All right, this is what happened. What can I do now?" The cancellation is still inconvenient. You stop making it worse by fighting a fact you cannot undo.
Reflection Question
What reality are you still arguing with in your head? If you stopped arguing, what could you do next?