Authors love comments! All comments! Right? Right! But! If you find yourself reading a fic and liking it but then all of your comments are unrelentingly negative, it can get a writer down, especially if they don’t get a lot of other people commenting. So while it’s fine to say, ugh, this character is such a jerk! I hate how he does that! This is so gross! etc. (when those things are intended to be gross and jerk-like), it makes it a lot easier for the author to feel good about the fic (and want to keep writing) if the comments also include something positive. “OMG, I love how realistic you made this--I could see how gross it must’ve been!” Or: “That character is such a jerk, I hope he gets what’s coming to him. Can’t wait to read more!” Seriously, it might not seem like a big deal but putting even the tiniest compliment in can make a huge difference to a writer who is struggling.