The Ender 3 arrived and I did what everyone does: assembled it in an evening, loaded the sample filament, and printed the little cat that comes on the SD card. It looked great. I was a genius. This was easy.
Then I tried to print something I actually wanted, and the wheels came off. The first attempt didn't stick and turned into a bird's nest of filament being dragged around the bed. The second curled up at the corners. The third looked promising for two layers and then the nozzle started ploughing through what it had just laid down.
All three failures were the same root cause, which I'd been ignoring because the sample cat happened to print fine: the bed wasn't level, and the nozzle was too far from it. Every guide says level the bed first. I, of course, knew better.
The fix was the famous paper trick. Cold bed, nozzle homed, then slide a sheet of paper under the nozzle at each corner and adjust the wheel until there's a slight drag. Round twice, because moving one corner nudges the others. Then a first-layer test print to confirm the lines are squished flat and fused, not round and separate.
The next print stuck like it had been glued down. Nothing about it was clever, it was just the step I'd skipped because the demo cat lulled me into thinking I'd cracked it. First prints, first failures, all of them mine.