When I am consumed by my problems -- stressed out about my life, my family, and my job -- I actually convey the belief that I think the circumstances are more important than God's command to always rejoice. In other words, that I have a "right" to disobey God because of the magnitude for my responsibilities.
Worry implies that we don't quite trust that God is big enough, powerful enough, or loving enough to take care of what's happening in our lives.
Stress says that the things we are involved in are important enough to merit our impatience, our lack of grace toward others, or our tight grip of control.
Basically these two behaviors communicate that it's okay to sin and not trust God because the stuff in my life is somehow exceptional. Both worry and stress reek of arrogance. They declare our tendency to forget that we've been forgiven, that our lives here and now are brief, that we are headed to a place where we won't be lonely, afraid, or hurt ever again, and that in the context of God's strength, our problems are small indeed.
Why are we so quick to forget God? Who do we think we are?
Crazy Love: Overwhelmed by a Relentless God
Francis Chan with Danae Yankoski, (c) 2008
David C. Cook, p.42
Guilty as charged here! Not sure I realized it was sin though.