Declining things at work without the paragraph of apology

Most of the difficulty is not the no, it is the amount of explaining people attach to it, which invites negotiation. Phrasings that hold up, from having got this wrong for years.

• "I can't take that on this week." Complete sentence. No reason attached. A reason is a thing to argue with; the absence of one is not rude, it just feels rude to the person saying it.
• Offer a when, not a why. "Not this week, but I could look at it Thursday" ends the conversation without either a justification or a flat refusal.
• Trade rather than refuse. "I can do that if X moves to next week, which do you want?" This is the one that works upward, because it hands the priority decision back to the person who owns it.
• For the ride home, the favour, the small thing: "I can't, sorry" and then say nothing. The silence is uncomfortable for about two seconds and it works. Filling it is what unravels every one of these.
• Say it once. Repeating the same sentence unchanged, without escalating and without new reasons, is the whole technique for someone who keeps pushing.

What backfires: an invented reason, because it can be solved and then you are trapped. Apologising more than once, which signals the no is negotiable. And saying "let me check", which is a yes with a delay and everyone knows it.

The thing that made this easier was noticing that the discomfort is entirely mine and lasts a few seconds, while the consequence of a soft yes lasts a week.