Those masterful images because complete
Grew in pure mind, but out of what began? (3.1-2)
Ah – here's where the real soul-searching begins. All his ideas and images seem real to him, because they are totally complete. But wait a minute, where did they come from in the first place? How do you trace the starts of your ideas? Once they're all pretty and shiny and bound up in leather books, it's hard to remember the half-sentences and unfinished thoughts that were once your inspiration. Notice Yeats's willingness to question himself at every turn here. That's the sign of a true explorer.