I was proofreading a paper for my friend yesterday. The paper is for a Spanish class we took together, and in parts I really couldn't understand what she was saying in the paper. When I asked her why none of the words made sense and asked if she translated it, she said, "Oh, I just pasted that quote in an online translation site." My eyes went bug-eyed and I said, "You can tell right away that this isn't a human translation." This got me thinking to when I was in high school and my teacher said "Never never NEVER put your whole paper in an online translation site!" and we thought he was crazy and could never tell.
Now for my question: Were you told something in school that you thought was silly and later found out that the teacher made a good point? If yes, what was it?