Ooohhh I had some dumb tax trouble this year!! Completely my fault, too.
For context, I separate my personal freelance dealings from my comic/merchandise sales, so for the latter I have an LLC with a couple partners. None of us get paid a salary or anything from business, but we like to keep the comic money separate. Unfortunately I didn't do enough research on the subject and I filed my personal taxes BEFORE my business ones, thinking "Oh I don't have any income from it so it shouldn't affect things".
I was wrong. :[ My business partner was like, "Hey uh, hope this doesn't mess you up, but apparently we have to do the business taxes before we file our personal ones because it adds an additional form." Cue me pulling my hair out because I paid $100 for H&R Block and I'll probably have to pay them AGAIN to amend it and send it in. :[[[[[ AUGH I'M SO MAD AT MYSELF.
A general tax note though, I was really mad at the online tax services because they were never upfront about how much they were charging if you had more than a W-2, and only said "Yeah it's TOTALLY free... EXCEPT IF YOU WANT TO ADD ANYTHING EXTRA," once you've already filled out all your prior info and made an account and blagfbshjshsa waste of my time.