Writes a pretty pessimistic piece (5)
I believe the answer is:
types
'writes' is the definition.
(typing is a kind of writing)
'a pretty pessimistic piece' is the wordplay.
'piece' says the answer is hidden in the clue.
'TYPES' can be found hidden inside 'pretty pessimistic'.
(Other definitions for types that I've seen before include "Sorts; kinds" , "Sorts - varieties" , "Characters" , "Uses a keyboard to write" , "Uses a keyboard; sorts" .)