Character is knowing there are things you will not trade, even when the offer improves.

Having things you will not trade at any price is what makes you difficult to move. Offers improve, pressure increases, and if everything has a number then eventually the number arrives. Naming a few things as unavailable is not rigidity; it is what keeps you from being slowly bought.

Write down two or three things you will not do regardless of the offer. Be specific rather than lofty. Then, when an offer comes that would require one of them, you are not deciding under pressure with a good reason in front of you. You are just consulting a decision already made.