Plain?

Why is it that my eye So oft plays tricks on me-- That when I look onto a plain It's nothing plain I see? What was it 'bout the whistling wind That someone found a bore? What was it 'bout the dancing grass That someone thought so bare? Why was it that he overlooked Those brilliant skies of blue? Why was it that he forgot Those flowers of every hue? Someone else made it; Someone else cast its frame. So by what right I ask, pray tell, Did he call it plain?