Your excuse might be true. It still isn’t useful.

A reason can be completely accurate and still leave you exactly where you are. The tiredness is real, the schedule is real, the thing that happened was not your fault. None of that is in question, and none of it moves the situation on its own, because explaining and progressing are two different jobs.

Take the honest reason and add one question to it: given that this is true, what is still possible. Maybe it is a smaller version, or a later start, or asking somebody for help. The reason stays true, you just stop letting it be the last line.