As the role is complicated, despair (4,5)
I believe the answer is:
lose heart
'despair' is the definition.
(both can mean to feel hopeless)
'as the role is complicated' is the wordplay.
'is complicated' indicates anagramming the letters (a complex or confusing ordering of the letters).
'as'+'the'+'role'='astherole'
'astherole' anagrammed gives 'LOSE HEART'.
(Other definitions for lose heart that I've seen before include "Become despondent" , "Mislay a card" , "Falter in courage - or fall in love? (4, 5)" , "Here's a lot to cause courage to ebb" , "get discouraged?" .)