I think it's quite interesting that W.B.Yeats insisted to stick to the "rules", for no other reason than he feared the mortality of his poems. "All that is personal soon rots; it must be packed in ice or salt." He loved poetry with all his passionate heart, to the point that he assumed that poetry lines were like stomping hearts. But, he wanted to pour Formalin in the glass vessels containing these hearts, in order to reserve them for future generations...