What does it mean: a lost cause?

[Rusalka]

Test No. incompl/inter-61 "Losing It (1)", question 8

After he'd wasted all his money, got into debt and then ended up in prison, his family began to regard him as a bit of a lost ..........

(a) case
(b) reason
(c) cause
(d) argument

Test No. incompl/inter-61 "Losing It (1)", answer 8

After he'd wasted all his money, got into debt and then ended up in prison, his family began to regard him as a bit of a lost cause.

Correct answer: (c) cause

Your answer was: n/a
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What does it mean??
_ lost cause_????

[Alan]

Someone who cannot be helped.
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English as a Second Language
You can read my ESL story A day in the life of a parliamentary candidate