You cannot make the plan, and delaying the message feels briefly easier than sending it. The longer you wait, the more awkward it becomes—and the less time the other person has to adjust.
Tell them as soon as you reasonably know. State the change clearly, acknowledge any inconvenience and provide the relevant explanation without inventing details. If tickets, bookings or shared costs are involved, address those arrangements directly and follow the applicable terms.
If you genuinely want to meet another time, offer a realistic alternative. Avoid saying “We must reschedule” automatically when you have no intention of doing so. A clear cancellation is more considerate than adding another vague promise to soften it.
The amount of repair depends on the situation. Canceling a casual coffee is different from withdrawing from something someone relied on you to help deliver. Consider what information, handover or practical contribution is reasonably needed.
Accept that the other person may be disappointed. You can understand that reaction without reversing a decision that is necessary. Equally, a valid reason does not erase every consequence of the change.
If cancellation has become a pattern, look at how you are agreeing to plans. You may be accepting too quickly, choosing unsuitable times or trying to maintain a level of social activity that does not fit your circumstances. A smaller reliable plan may serve the friendship better.
Check what has already been committed. A casual walk and a prepaid booking carry different practical consequences. Give notice as soon as you know, and address any costs or arrangements for which you are responsible. Keep the message clear enough that the other person understands the plan is canceled, rather than leaving them unsure whether to wait while you decide how you feel.
Offer another date only when you genuinely intend to arrange it. If the problem is that the current kind of plan rarely works for you, propose a different shape rather than repeating the same cycle. You can be honest about needing a lighter commitment without supplying a private explanation in full. Reliability sometimes means making smaller promises, especially when enthusiastic invitations repeatedly become difficult to keep once the day arrives.
When you do meet again, let the visit be about the present rather than repeatedly returning to the apology. The practical aim is a relationship in which changes can be communicated honestly and commitments remain broadly trustworthy. Nobody can promise never to cancel. You can make it less likely that the cancellation also contains avoidable uncertainty, silence or work the other person was left to discover at the last moment.
A little more room to be yourself.