We justify our road rage because the street is filled with "bad drivers." We excuse our impatience because the lines were too long or the service was too slow. We rationalize our jealousy and insecurity because it's obvious that we deserved the promotion and not the other person.
Part of the issue here is that there is a hint of truth in each of these justifications. Enough truth to keep us from looking at our own selves. The real truth is that sin originates in you. Circumstances can certainly play a role, but the choice to sin is our own. The bad driver makes you angry, but the anger is already present in your own heart. The service may be slow and you may have deserved the promotion, but the impatience and pride is inside of you.
Circumstances bring to surface what already dwells in our hearts. No one can provoke inside of you what does not originate there. Every human heart (including my own) needs sanctifying. We need God's grace to change us in deeper ways then we can imagine.
We really should thank God for the person (or circumstance) that exposes our sinful tendencies. That person reveals what's really in our heart and shows us areas where we still need to grow. Only by seeing our true selves and seeking God's grace can we begin to change. Blaming someone else may make us feel better, but it won't solve the real problem.