“There is nothing so broad and so open in the world through which the vanity of our judgment does not creep.”Michel de Montaigne · Eseuri · 1580 · II, 12
A field's clarity doesn't purify judgment: vanity seeps in even where your evidence is strongest.
Montaigne notices that even the clearest, most verifiable fields are not safe from presumption. The mechanism is simple: the mind mistakes its own assumptions for reality and projects them everywhere, including where they could easily be disproved. An astronomer who charts precise orbits may still make unwarranted claims about the character of someone he has just met. The openness of a terrain guarantees nothing about the modesty of the one crossing it.
Montaigne adds an uncomfortable detail: vanity is strongest exactly where we cannot easily be corrected. A doctor may be cautious about a diagnosis, yet feels free to judge politicians or a neighbor's marriage with a confidence nobody can challenge on the spot. Real, checkable competence stops at the edge of its own field. Beyond that line lies open ground for assumptions. An economist who reads budgets flawlessly does not thereby know better than you how to raise your child, yet will say so anyway. The useful question is not what I know, but where what I know ends. But how do you spot that boundary in your own mind, without an outside observer?
Why it matters It reminds you to check whether a firm opinion you hold, even in a field you master, is not just vanity dressed up as competence.