Agreeing to something you can’t finish is worse than saying no up front. People plan around your yes.

A yes is something other people build on. When you agree, somebody stops looking for another solution, plans around your part and then finds out late that it is not coming, which leaves them worse off than a no would have. Declining up front feels unhelpful and is often the most useful thing available. Honesty about capacity protects everyone, including you.

Before you agree to the next thing, look at the week it lands in. If it will not fit, say so now rather than hoping. A clear no today is kinder than an apology on Friday.