Let the student know if "this is just a demo for fun, give it a shot" or "this is pretty important in your development, you should be able to do this in order to tackle future lessons"
I'm currently in the 'Rock 1' section, and have been wondering the same, but I'm content with assuming that, with practice, I'll be able to do 'that' one day, and trying to not get hung up on the one thing I can't do yet.