“Being more successful than is good for you” is overstating it (5,3,3)

'being more successful than is good for you is overstating it' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'being more successful than is good for you is overstating it' is the wordplay.
I cannot quite understand how this works, but
'successful' could be 'in' ('in' can be similar in meaning to 'successful') and 'in' is present in the answer.
'good' could be 'g' (abbreviation) and 'g' is found within the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is located in the answer.
'being' could be 'goof' (goof is a kind of being) and 'goof' is found in the leftover letters.
The remaining letters 'oar' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?