When we are simply imagining chilling scenarios, we are facing the horrible emotions without any of God’s sustaining grace. Every time we imagine something, we put ourselves through agony of a kind we will never have to go through in real life. Because when awful things are actually happening, God walks with us through them and gives us His grace and strength. The peace of God’s presence through a trial is something I can never conjure up in my imagination, and something that only comes with real trials, not the pretend ones I make up while driving.
Worry really doesn't serve us well. God calls us to live in each moment--which means to take the time and energy to actually be present in each moment. And each day has enough troubles of its own . . . when we actually go to the trouble enjoying God today, it doesn't leave us with time or energy to be making contingency plans for all sorts of situations which will never actually happen.