The friend who accepts a changed plan kindly has made future honesty less frightening.

How someone responds to a cancellation teaches you what it will cost to tell them the truth next time. A warm reply makes honesty cheap, and people who feel safe canceling tend to cancel less and lie about it never. A sigh, a joke with an edge, a long silence: all of these get remembered and quietly push the next person toward a vague excuse. You are always training each other in what can be said.

When someone changes a plan on you, make your first response an easy one. Then notice how the people you cancel on respond to you.