Excuses make you feel better. They don’t make anything better.

An excuse does a real job, just not the one you want. It lowers the discomfort of having fallen short, which is why it comes so quickly, and it leaves the actual situation exactly where it was. The assignment is still unfinished, the shift is still uncovered. You have treated the feeling and left the problem.

Notice the moment you start explaining and ask what the next useful action is instead. Say the short version and move: I did not get it done, here is when I will. Reasons are worth giving when they help someone plan, not when they are there to make you feel better.