Crossword Genius

The poor fellow can't do any good (6)

Ross

I believe the answer is:

sinner

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'the poor fellow' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps there's an association between them I don't understand?

I cannot understand how the rest of the clue works.

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(Other definitions for sinner that I've seen before include "Immoral transgressor" , "One in breach of moral law" , "Wrong-doer" , "One morally corrupt" , "Evildoer" .)

I've seen this clue in the Evening Standard.
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