We may not understand the reasons for our dislike or growing discomfort, but we will be troubled by incongruity. Actually, it was not what was missing but what was excessive. Size is not the only determinant of distance. Our brain does a great job of filtering and interpreting so that extraneous visual information is subdued or eliminated depending on the situation.
It's in the details
Driving on a busy highway, we are most acutely aware of elements in our immediate environment, such as the cars or people around us that may impact our safe travel. Second to that we take in what is beyond, such as red lights ahead or people dashing out unexpectedly.
Beyond that, in less detail, are the surroundings as far as our eye can see. From those distant surroundings, vehicles, people, buildings, birds, animals, clouds are all filtered out of our consciousness to enable us to get to our destination without being overwhelmed by extraneous information. Simply put, objects on which we focus our eyes are sharply defined while surrounding objects are less clearly defined and objects further away from our area of focus are blurred.
What you see
The third aspect of landscape painting that was truly our 'aha' was Ed's explanation of atmospheric or optical perspective. Unless we have a foggy or smoggy day, the air between you and me as we meet on the street is invisible and, as human beings, we tend to think that what we cannot see has no real substance: like the air in our atmosphere, for instance.
But, as we know, air does have density and as distance and the layers of atmosphere between ourselves and objects increase, the atmosphere acts as a filter between viewer and object. Of the yellow, red, and blue triad, the first to be filtered out are the yellows, followed by the reds, until we are left with only the blues.
That is why trees, mountains, or other objects appear purplish or blue in the far distance. Beyond that, when the blues are also filtered out, all things still visible are reduced to a nondescript pale grey. Similarly, on a clear, sunny day, the sky at the far distant horizon appears a pale grey because of the thicker atmospheric layer that separates us from that distant horizon. On the other hand, looking straight above our head, through a lesser atmospheric layer, we see the sky as a dark ultramarine blue.
Blue Sky Horizon, Image by Ryan Grobin
In a landscape painting, an artist takes us on a journey into a canvas and it is his/her level of skill that will encourage us to linger and roam around awhile before we move on. It is the artist's job to edit all the extraneous detail from a landscape so that we really can see the tree in the forest. The composition will provide this map into and around the canvas.