Finally The Observer covers men being plagued by pessimism (6)
I believe the answer is:
eeyore
'plagued by pessimism' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'finally the observer covers men' is the wordplay.
'finally' says to take the final letters.
'observer' becomes 'eye' (I've seen this before).
'covers' means one lot of letters goes inside another.
'men' becomes 'or' (military abbreviation for Other Ranks).
The final letter of 'the' is 'e'.
'eye' going around 'or' is 'eyore'.
'e'+'eyore'='EEYORE'
'being' acts as a link.
Can you help me to learn more?
(Other definitions for eeyore that I've seen before include "Gloomy donkey in Winnie-the-Pooh books" , "Christopher Robin's dismal donkey" , "Pooh's sad friend" , "miserable ass" , "Literary donkey" .)