Glider Insider
I don't think you ever chill but you become more confident in you own ability to recognise a bad situation that will turn to pot quickly that the student won't learn from and will require your input. And likewise you will recognise a situation that will turn to pot but the student will learn from and won't require you taking over.
Those three words that Zeke uses are great.
And if you are having problems with a student not getting the landing always talk to your CFI. I had a student that was doing really well but when it came to the flare would botch it up every time and I couldn't work out why. After talking to my CFI we had a potential solution and when I took the student out again for circuits and taught him this new approach he nailed it. I can still see the grin on his face. From that point on I always talked to my CFI about problems with students.
Talking about flying with experienced pilots, I find some of the scariest pilots to fly with intially are airline pilots that are coming back to fly lighties to get some hands on flying again. Flaring at 50ft and pushing the nose abruptly foward on touchdown certainly keeps you awake!!