I was tired and hung-over when I was shocked into realizing how big the discrepancy was between viewing a piece of art in my textbook from school and real life.
It's slightly better now with the Internet and HD quality resolution screens but it's still not quite the same.
For me this was brought into clear focus by seeing Rembrandt's "The Nightwatch".
It was huge. Easily as tall as me (I'm about 6 foot 4) and several feet wide.
The paints vibrant.
And the shading and light, gave the feeling of 3D.
At that point I got it:
You don't have to care anything about the painter - to be affected by the art.