In the flowchart of choice, the unbeliever also has but one choice and he was born into it. All the other ensuing decisions are constrained by that one choice.
We have to make an ultimate/supreme choice to live for Self or God (heart/purpose in life). Motive is more important than conduct. Our subordinate and simple choices may or may not line up with this at any given time. We are not born with a causative nature or born again with a causative nature. Choices flow from will and mind, so we are responsible. Our choices lead to habits, nature, character, but they are still not causative. An atheist can remain faithful in marriage and a Christian can commit adultery. We cannot save ourselves, but we can receive or reject Christ who does save or condemn us.