Never wait until that usually easygoing person starts to argue with you.

Before that, every one of their concessions is actually a sign of giving you face and considering your feelings;
and when they start to argue, it's no longer pettiness, but a reminder of boundaries, indicating that you have already disappointed them deeply, and there is little left of their place in their heart.
People's hearts are always mutual: how you treat me, I will return the same to you.
If you are not cherished, you will gradually become distant;
if you are not valued, you will only start to see it as less important over time.
And once such a person truly turns hostile, it often means a complete farewell.