From Stephen Botterill's introduction to Dante's De Vulgari Eloquentia:
"...in the aftermath of the disappointment of all his most cherished hopes for earthly success [ca. 1303], Dante underwent at this time an experience of profound and searching self-examination, which led him to try to rebuild the moral and intellectual structure of his personality from the foundations." (xiv)
I have two immediate reactions to this claim. The first is epistemological. How can we know such things? (Botterill explains that we know that he did a lot of reading at this time, and infers the rest "from later developments".) The second is wonderment at the idea of responding to a total failure in public life by rebuilding one's personality from the ground up.