Why is so much of teaching filled with fear?

No teacher has ever completed a school day with every item on their ‘to do’ list fully ticked off. It’s pretty much impossible to do the job as thoroughly as you’d like to, and there’s a constant feeling of guilt (you know the one I mean, don’t you) that you’re letting somebody somewhere down. “If only I had more time, if only I could do more,” goes the familiar nagging feeling. “What if somebody finds out I haven’t done that particular job?”

Why is so much of teaching filled with fear?.