You can’t be a “Yes” if you can’t say “no”.
What does that mean?
When we are not able to freely and easily say “no” to a proposal, if we say “yes” then that yes is not a full yes, a full yes as in a yes in every cell of our bodies YES. It’s a yes with some resentment, or fear, or obligation. It’s a “yes” with an “I’ll get you back for this” underneath. A “yes” that you’ll be discussing for years afterwards, and not in a good way.
Is that what you really want? If not, then you better get good at saying “no”.
It was when my primary girlfriend and I got good at saying and hearing “no” that things got much easier for us. Communication got easier, less charged. More information would come out more easily. Negotiating alternatives became simpler. In general, “no” doesn’t end a conversation, it really starts one, as long as you don’t get stopped or shut down by the dreaded “no”.
Another good thing that came of it was that when I found that she could easily and pleasantly hear and accept when I was a “no” to something, it made it much easier for me to change my no into a yes. Somehow knowing that I could say no and have her respect it, even enjoy it(!) made me want to reconsider my no. Many times my initial no became a yes after just 10 or 20 minutes. After some years of this, I can say that there used to be times that I regretted saying yes, but the times when I said no and then changed it to a yes never came back to haunt me.