Double Vision

What is it with poets and doppelgängers? From a letter from Lord Byron to John Murray, Oct. 6, 1820:

In the latter end of 1811, I met one evening at Alfred my old school and form-fellow, … Peel, the Irish secretary. He told me, that, in 1810, he met me, as he thought, in St. James’-street, but we passed without speaking. He mentioned this, and it was denied as impossible; I being then in Turkey. A day or two afterwards, he pointed out to his brother a person on the opposite side of the way: ‘There,’ said he ‘is the man whom I took for Byron.’ His brother instantly answered, ‘Why it is Byron, and no one else.’ But this is not all:– I was seen by somebody to write down my name among the inquirers after the king’s health, then attacked by insanity. Now, at this very period, as nearly as I could make out, I was ill of a strong fever at Patras, caught in the marshes near Olympia, from the malaria. If I had died there, this would have been a new ghost story for you.

Similar experiences befell Shelley, Goethe, John Donne, and Wilfred Owen.