It's difficult to be hard and inflexible (5)
I believe the answer is:
stiff
I believe this is a triple definition!
'it's difficult' is the first definition.
(I've seen this before)
'to be hard' is the second definition.
(similar in meaning)
'and' is a link.
'inflexible' is the third definition.
(similar in meaning)
(Other definitions for stiff that I've seen before include "Starched, rigid" , "18 [HARD]" , "Unfriendly" , "Frigid" , "Difficult" .)