Difficult? That’s your hard luck! (5)

I believe the answer is:

tough

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'difficult?' is the definition.
('tough' can be similar in meaning to 'difficult')

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for tough that I've seen before include "Rough, violent; strong" , "Resilient; thug" , "Unlucky" , "Taxing" , "Strict, uncompromising" .)

I've seen this clue in the Evening Standard.

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