After some errors, he's simply finished (4)
I believe the answer is:
rory
'after some errors he's simply finished' is the definition.
The definition suggests a singular noun which matches the answer.
'after some errors he's simply' is the wordplay.
'after' says to put letters next to each other.
'some' means to look at the middle letters.
'he's simply' becomes 'ry' (I can't explain this - if you can you should give a lot more credence to this answer).
The middle of 'errors' is 'ro'.
'ro' put next to 'ry' is 'RORY'.
Can you help me to learn more?
(Other definitions for rory that I've seen before include "Gaelic man?" , "Male" , "Irishman" , "Form of Gaelic name Ruairidh, rhymes with Conservative" , "Fellow" .)