Lesson 1 in Metalwork class when I was 12yrs old. And yes, the outcome was demonstrated and another lump taken out of the floor. I've used lathes on and off all my life, and have had my own in the garage for 30yrs. I can guarantee I've NEVER left the key in the chuck.
I have seen chuck keys fitted with a spring at the bottom meaning the key will not stay in the chuck without being pushed in. I have been known to launch a key across the workshop if I found it left in place. Saves it knocking lumps out of the bed
