I want to fire my assistant on the spot
Why do they need to be fired?
Yes, he an idiot and he makes my life harder with his stupid mistakes.
You have responsibilities and needs. If your assistant is not giving you that. You have the right to look for another one.
You might be right, but it's too hard to find a good one.
You can always host some interviews then. I do not blame you for wanting to fire them if they are just making your life harder.