Further to perception, another interesting concept is perspective.
Based on perspective – even a tree may look bigger than a huge mountain. If that were the case, one may focus on the tree and not on the mountain. Another way of looking into it is – whatever is near to us may affect us more.
Further, it is natural that the thing/fact that affects us more – gets more focus – gets appropriate response – when it comes to problem solving. The solved problem disappears from our mind/sight – with appropriate blinks/memories.
As, in the given picture, trees appear moving fast – also disappear fast. While things away – with less focus – remain there for a long time – unattended – like, mountain in the picture.