As a French, "no" comes easily. I'll try to explain what I believe when I say no. I think the important thing is that it must be clear why you say no, which me

As a French, "no" comes easily. I'll try to explain what I believe when I say no. I think the important thing is that it must be clear why you say no, which means explaining your reasons so that others either agree with you, or chose to camp on their decision while knowing fully that it's just an opinion and not a fact. "No" is a recap of your thinking, so you need to lay out all the work that led you to this conclusion. When people understand it's not about them, they might not take it as personally and take a step back. It's even better to be constructive (because "no" shouldn't mean "I don't like you" but "this is not the best way"). A method I've learned about is the "Yes! No. Yes?" (https://www.fastcompany.com/3026980/yes-no-yes-how-to-turn-someone-down-without-ruining-your-relationship https://www.fastcompany.com/3026980/yes-no-yes-how-to-turn-s...). The idea is basically what I said above: make the other person understand that the exact thing you're talking about is not possible, but that doesn't mean you reject them as a person and you're not open to change. You're closing a door but you're not barricading the house.