I think this illustrates the sorry state of education. I learned about unknown unknowns in high school from Socrates. I hope my son learns them even sooner. There's an opportunity cost in false confidence. Better to get that out of the way at a young age, and learn to feign confidence when necessary.

But that isn't everything. At a university you start to see that subjects that might have appeared to be shallow at first glance are really quite vast and complex. It's hard to say with confidence you are an expert on any of those subjects after seeing a little ways down their respective rabbit holes (which you rarely get the opportunity to do in high school).

Which is exactly why I love this stanza from Pope's Essay on Criticism[0]:

A little Learning is a dang'rous Thing;

Drink deep, or taste not the Pierian Spring:

There shallow Draughts intoxicate the Brain,

And drinking largely sobers us again.

Fir'd at first Sight with what the Muse imparts,

In fearless Youth we tempt the Heights of Arts,

While from the bounded Level of our Mind,

Short Views we take, nor see the lengths behind,

But more advanc'd, behold with strange Surprize

New, distant Scenes of endless Science rise!

So pleas'd at first, the towring Alps we try,

Mount o'er the Vales, and seem to tread the Sky;

Th' Eternal Snows appear already past,

And the first Clouds and Mountains seem the last:

But those attain'd, we tremble to survey

The growing Labours of the lengthen'd Way,

Th' increasing Prospect tires our wandering Eyes,

Hills peep o'er Hills, and Alps on Alps arise!

[0]: http://poetry.eserver.org/essay-on-criticism.html

A counter-quote:

"A little learning is not a dangerous thing to one who does not mistake it for a great deal." -- William A White

sometime, when I read a comments in hackernews, I know that I don't know so many things :)