What does it mean that the cost of overcommitment?

Exceeding capacity produces lower-quality outputs more errors and eventual burnout.

Example: You pride yourself on being the person who says yes. A colleague needs help with a pitch deck — yes. Your manager asks you to lead a cross-functional initiative — yes. A friend wants feedback on their business plan — yes. Within two months you are nominally contributing to eight projects. You deliver all eight. But the pitch deck has a calculation error that costs the deal. The initiative launches a week late because your status updates were shallow and missed a dependency. The business plan feedback is generic enough to be useless. Three of the eight people you helped would have been better served by an honest no, because what they got was the appearance of help without the substance of it. Your reputation — the thing you were trying to protect by saying yes — took more damage from eight mediocre contributions than it would have taken from five polite declines and three pieces of excellent work.

Try this: List every active commitment you currently hold — professional projects, personal promises, recurring obligations, informal agreements. For each one, rate the quality of your current contribution on a 1-to-5 scale (5 = work you are proud of, 1 = you are embarrassed by it). Count how many are at 3 or below. Now ask: if you could only keep half of these commitments, which half would you choose? Notice the gap between what you are carrying and what you can carry well. Write one sentence: 'I am currently committed to [X] things, [Y] of which are receiving substandard effort.' That sentence is your overcommitment diagnostic.