Decision that’s always wrong! (3)
I believe the answer is:
out
'wrong' is the definition.
(eg a calculation might be 'out')
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for out that I've seen before include "Dismissed, in cricket" , "on sale" , "Revealed; unconscious" , "Mistaken; unconscious" , "Free" .)