Like pretty much anything that involves a skill, from baking a cake to playing the mandolin to building a bicycle wheel to tuning an engine, making the perfect espresso drink can bring out the competitiveness and obsessive tinkering instinct to get it just a little bit more perfect this time. People just love tuning things.

Every step on your list involves technical decisions. The fineness of the grind affects the extraction (and changes with the temperature and humidity). Exactly how much coffee you put in the holder and how firmly and evenly you tamp it does too. The hot water (exactly how hot?) extracts about a zillion compounds from the coffee as it is forced through it, and small changes in things that affect that extraction have big effects in the resulting liquid.

Note that the temperature of the machine changes depending on how busy you are.

You have to know exactly when to stop extracting, too. You know the crema that forms on top of a shot? Leave it too long and it dissolves; too early and it doesn't form properly, and the coffee might be too bitter.

Steaming milk is a real art form. You'd know this if you had ever tried it; it's HARD to do it right, and even harder to fine-tune the foaming. You're holding the nozzle of steam (how hot?) just under the surface of the liquid milk, which you can't see because of the foam. Do it wrong and you burn the milk or worse fill it with water that isn't steam anymore.

The pour is important. Watch next time someone makes you a drink, and see how it mixes perfectly. If you've ever done it, you know that doing that little design flourish, the rosette or leaf or whatever, is simply impossible to even contemplate without special training, practice, and a real knack.

If you read books or magazines aimed at serious coffee heads, you'll see endless discussions about all of these points and more. They get really into it. It's not necessary to get to that level to make a good cup of coffee, but it's POSSIBLE. So people will do it.

I would say the biggest place to screw up is the steaming; that's the part that always gave me the most trouble (I was a mediocre barista on my best day, a terrible one more often). But even with a push-button machine it's pretty easy to pull a crappy shot if you don't know how to tamp or if your grind is wrong or if you run it too long.

Oh, and if your stuff isn't clean -- grinder, espresso head, steam wand -- you'll get nasty stuff too.