How hard it is to have eyes and see only the visible!                                  The essential thing is knowing how to see,

Knowing how to see without thinking,
Knowing how to see when you see,
And not thinking when you see
Nor seeing when you think.

But this (alas for those of us whose souls wear clothes!)
This requires long study,
An apprenticeship of unlearning.

The Complete Works of Alberto Caeiro by Fernando Pessoa