A clear limit protects the quality of the contribution you can still make.

Limits are usually framed as what you are withholding, when mostly they determine what is left. Say yes to everything and the quality drops across all of it, so the people who most needed your attention get the same thin version as everyone else. A boundary is what keeps the remaining contribution worth having.

When you decline something this week, say what you are protecting rather than only that you are full. Offer the smaller version you can genuinely do well. People accept a clear limit far more easily than they forgive work that arrived late and half finished.