It's a mistaken conclusion, you know (3)
I believe the answer is:
ken
'know' is the definition.
(I've seen this in other clues)
'it's a mistaken conclusion you' is the wordplay.
'KEN' is hidden in amongst the letters.
However, I'm uncertain how the hidden word is indicated.
Can you help me to learn more?
(Other definitions for ken that I've seen before include "Awareness" , "One's range of knowledge" , "Identify; -- Livingstone" , "Know; man's name" , "Understanding - boy's name" .)