Hesitate: it’s hard to be positive (5)
I believe the answer is:
haver
'hesitate' is the definition.
(I've seen this before)
'hard to be positive' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'to be positive' becomes 'aver' (I've seen this in another clue).
'h'+'aver'='HAVER'
'it's' acts as a link.
(Other definitions for haver that I've seen before include "show indecision" , "Hesitate; talk nonsense" , "Be slow in making a decision" , "Talk foolishly" , "Act indecisively" .)