Dependability means the excuse may be understandable and the commitment still matters.

Reasons and obligations operate independently. Your explanation can be entirely legitimate and the other person is still left with a gap in their plans, and treating the good reason as settling the matter quietly shifts the cost onto them. Both things are true at once.

When you cannot deliver, offer the reason and then deal with the consequence separately. Say what you will do to make it right. That combination is what keeps an understandable failure from becoming a pattern.