A poem I learned in middle school and have subsequently never forgotten is Flying Crooked by Robert Graves. I really like the poem because the visual imagery is so potent. If you've ever seen one of these cabbage white butterflies in nature, the poem immediately calls it to mind.

Flying Crooked

The butterfly, a cabbage-white,
(His honest idiocy of flight)
Will never now, it is too late,
Master the art of flying straight,
He has--who knows so well as I?--
A just sense of how not to fly:
He lurches here and here by guess
'Tween God and hope and hopelessness.
Even the aerobatic swift
Have not his flying-crooked gift.

-- Robert Graves