Pretty Good

[Grant Barrett]

There's an element to "pretty" that strikes me as a way of indicating that something
is sufficient for the purpose at hand, though not necessarily ideal, perfect or
total. This, to me is separate from pretty as a middling superlative.

Pretty ugly, then, might be saying "ugly enough to notice."

Pretty fair might be "sufficiently fair as to not cause debate."

Pretty tired might be "tired enough to take into account."