Elephants touch each other with their trunks. Monkeys engage in social grooming. Dolphins rub their flippers over each others' bodies. Animals constantly reassure each other with touch (scientists call it "affiliation"). We human animals often underestimate the need to put a verbal touch of reassurance into our communication with someone we disagree with. It's not caving in - it's actually a way of creating better energetic conditions for sorting out those disagreements.
Put a Yes before a No by making an effort to find and highlight the genuine common ground you share with someone before you deliver criticism. Can you validate their feelings? - "I get your frustration; I feel your disappointment". Can you identify a strength or a merit in what they’ve put forward? - "I appreciate the work you’ve put into this…" "I appreciate the level of detail in your rendering…"