But why would those "measurable statements and artefacts" lead one to believe they are competent? Presumably, wouldn't they also provide evidence of one's ignor

But why would those "measurable statements and artefacts" lead one to believe they are competent? Presumably, wouldn't they also provide evidence of one's ignorance if they were evaluated objectively? (If it wasn't clear, I'm poking at the idea that we have numerous biases that prevent objective evaluation)