Pushback framed as tradeoff is easier to hear than pushback framed as refusal
A flat “that is not possible” invites an argument. The same concern, framed as a tradeoff someone else gets to decide, invites a conversation instead.
Make the tradeoff visible
“I can fit that in, but something else will need to move. Which one?” This hands the decision back to the person making the request, which is usually exactly where it belongs.
Name what changed, not just that it is hard
“That timeline works for the original scope, not this new version of it.” This is not a complaint about difficulty, it is a factual statement about what changed, which is much harder to argue with.