Robinson Crusoe was once this unsuccessful (6-2)
I believe the answer is:
washed-up
'unsuccessful' is the definition.
(similar in meaning)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for washed-up that I've seen before include "as restaurant's dishes should be?" , "Done for" , "Successful no longer" , "Finished" .)