I was making pickles at home and forgot to weight them down in the jar. Two days later, the top layer was covered in white fuzz and I had to dump the whole thing. It really opened my eyes to how easy it is to mess up. Now I never skip using a fermentation weight to keep everything under the liquid.
TEMPERATURE plays a huge role too. My ferment went bad in just a day because my apartment was like a sauna. Now I keep it in the coolest spot I can find.
Wow, temperature really can make or break a ferment. Tbh, I had a batch of kraut turn mushy last summer when my kitchen got too warm. Now I'm paranoid and check the spot with a thermometer before I even start.