in Thoreau’s Journal:

There is some advantage, intellectually and spiritually, in taking wide views with the bodily eye and not pursing an occupation which holds the body prone. There is some advantage, perhaps, in attending to the general features of the landscape over studying the particular plants and animals which inhabit it.

A man may walk abroad and no more see the sky than if he walked under a shed. The poet is more in the air than the naturalist, though they may walk side by side. Granted that you are out-of-doors; but what if the outer door is open, if the inner door is shut! You must walk perfectly free, not prying nor inquisitive, not bent upon seeing things. Throw away a whole day for a single expansion, a single inspiration of air.