I had a coffee setup I was happy with for years. Then someone mentioned, in passing, that the grinder matters more than the machine, and I did the thing I always do, which is treat an offhand remark as a research project.
The claim turns out to be true, annoyingly. The grinder is where the consistency lives. A cheap blade grinder produces a chaotic mix of dust and boulders, and that range means parts of the same shot over-extract while other parts under-extract in the same cup. The dust goes bitter, the boulders stay sour, and you taste both at once. A decent burr grinder narrows the distribution, and suddenly the variable you were blaming on the beans was the grind all along.
So I read about burr geometry, flat versus conical, retention, single-dosing, and the difference between adjusting by steps and adjusting steplessly, until I had absorbed a frankly embarrassing amount of opinion about a kitchen appliance. I bought a better grinder. It was more than I meant to spend and the coffee is genuinely better, which makes it hard to be cross about.
The honest part is that the cup I had before was fine. Nobody complained. But "fine" is a dangerous word around a tinkerer with a free Sunday, and now I own a grinder I will defend at parties. Worth it. Don't ask what it cost.