I fix other people's 3D printers for a living, and almost every session ends at the same three numbers. Not a new printer, not a firmware flash. Three numbers.

1. Nozzle-to-bed gap on the first layer. Most people level the bed and stop. Print a single 0.24mm layer square in each corner and look at it from the side: you want the lines squished into each other with no gaps and no ridges. If you can see the bed between lines, you are too high. If the surface looks glossy and rippled, you are too low.

1. First layer speed. Everyone runs 60mm/s+ because the slicer default says so. Drop the first layer to 20mm/s. That one change fixes more adhesion complaints than any glue stick, hairspray or new build plate people buy first.

1. Retraction distance vs your hotend. Stringing is not a temperature problem as often as people think. Direct drive wants roughly 0.5-1mm, Bowden wants 4-6mm. If you are running a Bowden setup on direct-drive defaults, you will get webs between every tower no matter how cold you print.

The pattern I see over and over: someone buys a $40 upgrade to solve a problem that was a $0 setting. Change one variable, print the same small test, write down what happened. That is the whole job.

If your printer is failing in a way that does not match any of the three, it is usually mechanical - a loose belt, a worn nozzle, or moisture in the filament. A spool that sat open for three months will hiss and pop while printing, and no setting fixes wet PLA.