Reading the complete works of a poet is a different project from reading their selected works. The selected works — curated by the poet or by editors — give you the best version of the poet's achievement. The complete works give you the full range, including the work that failed.

Seeing the failures is useful. You understand the writer's preoccupations more fully because you see what they kept trying and didn't achieve. You also develop a more honest relationship to the work — you stop treating the best poems as inevitable and start understanding them as outcomes that were earned from processes that often produced worse outcomes.

I've read the complete poems of three poets: Emily Dickinson, Philip Larkin, and Wallace Stevens. Each complete reading produced a different poet from the selected reading. The complete Stevens is more anxious and more repetitive and more magnificent than the Selected.