Fail to understand and so annihilate (13)

'annihilate' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'fail to understand and' is the wordplay.
I cannot quite understand how this works, but
'fail' could be 'go' (synonyms) and 'go' is found within the answer.
'understand' could be 'ken' (I've seen this in another clue) and 'ken' is found within the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

'so' is the link.

Can you help me to learn more?