The printer arrived, I built it over an evening, and I printed the obligatory test cube. The cube was fine. Everything after the cube was a learning experience, which is the polite phrase for a small pile of failed prints in the bin.
The first failure was the classic one: a print that wouldn't stick. Three layers in, a corner lifted, the part started dragging round with the nozzle, and within a minute I had a tangle of plastic spaghetti welded to the head. Every guide says the same thing and they're all right: it's the bed. Mine wasn't level, and "level" turns out to mean a very specific gap between nozzle and bed, the thickness of a sheet of paper, checked at all four corners. Once I actually did the paper trick properly instead of eyeballing it, first layers started going down clean and the lifting stopped.
The second failure was subtler. Prints came out covered in fine hairs, little wisps of plastic strung between separate parts of the model like a spider had got at it. Stringing. The fix was dropping the hotend temperature about ten degrees and turning on retraction, so the extruder pulls the filament back slightly during travel moves instead of oozing. Cleaner travels, no webs.
None of this was exotic. No firmware, no mechanical fault, no exotic calibration. Just a bed that needed levelling and a temperature that was a touch too hot, both of which the manual told me and neither of which I believed until I'd printed the evidence. The cube was beginner's luck. The failures were the actual lesson, and they were cheaper than they looked: a few grams of filament and an evening to learn that the machine was fine and I was the variable.