Shared plans need updates when they stop being realistic
A commitment becomes easier to rely on when changes are communicated early. If you know you cannot reach a meeting by six, saying so before six gives the other person choices. An update cannot remove every inconvenience, but it prevents avoidable waiting and uncertainty.
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Information is part of keeping a commitment
You agree to meet someone at six. By five, it is clear that your earlier task will run late. Waiting until the meeting time to explain leaves the other person planning around information you already know is outdated.
An early update returns some choice to them. They can leave later, change the location or decide whether to reschedule.
A useful message states what changed, gives a realistic estimate and asks whether the revised plan still works. Repeatedly sending optimistic estimates can create more uncertainty than one honest revision.
The delay may remain inconvenient. Clear communication does not erase that effect, but it gives the other person a chance to organise their own time instead of waiting without context.