Manually identify the longest sequential task chain determining total project duration — delaying any one delays the whole delivery.

Repeat the same refusal in the same words calmly, no matter how the other person reshapes the pressure.

Say no in three sentences: thanks, refusal, closing — with no "sorry" or justification.

Memorize one 7-word refusal sentence and rehearse it until it emerges automatically under pressure.

Say "no, I can't" — complete sentence. No explanation, no apology.

Task a separate team with attacking your plan as if they were a smart adversary — before reality discovers it.