If an apprentice shows any promise, he is not treated with kid gloves. He is put through the wringer. Many can’t take it. One cannot become skilled at a trade if he is going to take criticism personally.
With writing in the prose form it should be the same. (Poetry is quite different. I will address that elsewhere.) Whether it be a teacher, professor, mentor or school paper editor; if said expert offers praise where none is due because he wishes to spare the feelings of the writer in hopes of establishing some confidence, what has been achieved? The novice has missed the opportunity to put some constructive criticism into practice and the professional has sacrificed his integrity.
When slush readers are being paid by the manuscript, it seems unlikely that they would sacrifice a regular tick on their tally sheets to send a piece back with a comment such as: “Maybe you should try painting,” It is incumbent on the teacher, however they might have earned that status, to give praise where it is due but also to smack the wrist when appropriate. As a teacher or mentor of writing, don't ever be afraid (as a master craftsman wouldn't) to say: "Do it over, and do it better."