Promises are forecasts. Patterns are the weather. Dress for the weather.

What someone says they will do is a prediction. What they have actually done twenty times is a record. When the two disagree, the record is the better guide, not because people are liars but because habits are stronger than intentions. Planning around the promise instead of the pattern is how you keep getting caught out by the same person.

Think about someone who keeps letting you down, and stop asking whether they mean it. Ask what they have done the last five times, then plan for that version: leave earlier, have a backup. You can still like them while being realistic about them.