“I can’t this time, but I can Saturday” keeps more friendships than a yes you can’t deliver.

A yes you do not deliver costs more than a no. Saying yes to protect the moment feels generous and then produces the cancelled plan, the unanswered message, the slow accumulation of evidence that you are unreliable, while a specific no with a date attached gives somebody something they can use. People forgive a no. They remember being stood up.

When you cannot do something this week, say so in the first reply and attach the alternative: name the day. Do not offer a maybe to buy time. Two sentences, sent straight away, protects a friendship better than a yes you will quietly undo.