What made you shift it back in? (6)
I believe the answer is:
motive
'what made' is the definition.
I can't judge whether this defines the answer.
'shift it back in?' is the wordplay.
'shift' becomes 'move' (I've seen this before).
'back' says the letters should be written backwards.
'in?' is an insertion indicator.
'it' in reverse letter order is 'ti'.
'move' placed around 'ti' is 'MOTIVE'.
'you' acts as a link.
Can you help me to learn more?
(Other definitions for motive that I've seen before include "Reason (for acting)" , "Purpose in doing something" , "Reason for doing something, perhaps a crime" , "Underlying purpose" , "Purpose - reason" .)