I bought a nicer bag of beans and expected nicer coffee. What I got was muddy, sour, slightly disappointing coffee made from expensive beans, which is somehow worse than the cheap stuff. So I did what any reasonable person does and assumed the problem was a piece of equipment I didn't own yet.
The reading all pointed the same way. Not the kettle, not the brewer, the grinder. My blade grinder wasn't grinding so much as smashing, producing a chaotic mix of dust and boulders. The dust over-extracts and goes bitter, the boulders under-extract and go sour, and you taste both at once. A burr grinder crushes everything to roughly the same size, and consistency turns out to be the entire game.
So I bought a hand grinder, told myself it was the sensible end of the rabbit hole, and now I own a little device that measures water temperature. I can see exactly where this goes. The coffee, in fairness, is genuinely much better, and grinding it by hand every morning is a small ritual I didn't know I wanted. I'll stop before the scales arrive. Probably.