You cant fix film with developer, I found out. I'm not sure how I got them confused, I wrote on the bottles in big giant letters...
Another time I'd just finished loading a roll of 120 onto the reel and taken it out of the changing-bag, and my mum ran in and told me the chimney of the house was on fire. We got it put out, but it was somewhat surreal.
I've only been at this for a few years though, I have plenty more mistakes to make.