Like luck, it can be hard (6)
I believe the answer is:
cheese
'like luck' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'it can be hard' is the wordplay.
I cannot really understand how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
'hard' could be 'h' (abbreviation used in pencil classifications) and 'h' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for cheese that I've seen before include "Big one's important" , "Eg Edam" , "Gloucester or Emmental, say" , "E.g. brie" , "product of cottage industry?" .)