Tags like "stupid," "bad at __", "sloppy," and so on, are ways of saying "You're performing badly and I don't know why." Once you move it to "you're performing badly because you have the wrong fingerings," or "you're performing badly because you don't understand what a limit is," it's no longer a vague personal failing but a causal necessity. Anyone who never understood limits will flunk calculus. It's not you, it's the bug.

-celandine13 (Hat-tip to Frank Adamek. In addition, the linked article is so good that I had trouble picking something to put in rationality quotes; in other words, I recommend it.)