Ironically, part of human carnality is our general unwillingness to give others the personal benefit of doubt. We are called to be optimistic about others in our relationships, and avoid undue cynicism and conspiracy theories, etc.
But another part of human carnality is our undue optimism over the goodness in our own hearts. More caution is needed. Our hearts need to be carefully guarded. We are so bad that we need to be forgiven and born again. We are needy for a Savior and Counselor.