Solve this . PS I made this myself.

Be you strong or weak ,
I am still your greatest strength.
Your will is my armor,
I cannot be bent.

If you are witty,
then your wit lies in me.
If you are shaky,
it's only because you've lost me.

Come come , don't be shy,
this last clue I give,
those who have me in excess sourly live,
What am I?