I think it's good to worry as well. It means you're thinking of all possible mishaps and are more alert/aware to avoid them. You just never know what could happen!
Last night I was walking my little weasels and I saw a "lost dog" posting. Domo the chi/terrier/others mix was apparently last seen outside our neighborhood liquor store (tons of pedestrian traffic and dog-owners around here).
It made me so sad to read that the owner is offering $3000 no questions asked. For such a large reward, I wish they considered that there are malicious people out there who steal dogs left outside in public and it wouldn't be worth the risk to lose him. Or, if I give mankind the benefit of the doubt, dogs can sometimes get loose and run away.
Poor poor little Domo away from home...