You mean a secondary cause like having a will of our own and being able to use it even when it doesn't line up with God's will? Wow, maybe that explains the existence of evil. I find it odd though why it's always solely our will when doing evil but solely God's will when doing good, it's like we all become robots under God's will.
God is the First Cause behind all grace, whether it be grace he actively bestows or grace he withdraws or withholds. In the case of the former God is due all the credit. In the case of the latter, the immediate/efficient cause of human will is ultimately responsible since God simply leaves fallen man in his immutable, hopeless and helpless condition to live his life in accordance with his sinful nature.