Don't understand why you turn a blind eye to (4,2,3)

'don't understand why you turn' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'a blind eye to' is the wordplay.
I cannot quite understand how this works, but
'a' is present in the answer.
'eye' could be 'see' (see is a kind of eye) and 'see' is found in the answer.
'to' is present in the answer.
The remaining letters 'fil' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?