I recently read Why Zebra's Don't Get Ulcers, Robert Sapolsky's classic book on stress and disease. While the book is over 15 years old, it is an entertaining and informative read. So why am I bringing up a book that wasn't even written this century? Well the prefrontal cortex, not well understood in the early 90s, offers an interesting perspective.
A calmly grazing zebra
The prefrontal cortex is the part of your brain that makes long term plans. Zebras don't have much of it, nor do they have much use for it. A zebra's life is simple. It mainly consists of grazing. It doesn't do much planning for the future. If it doesn't have food it doesn't worry that it will starve; it just keeps looking for food. If it feels a slight pain in it's tooth it doesn't have to worry that the pain will get worse and worse and require a root canal that it will be unable to pay for. It doesn't have a mortgage; it is already homeless and perfectly content. It doesn't worry about earning the respect of its co-workers, friends, children ... In fact zebra's don't worry much about anything. Their brains are not designed to worry the same as ours. And yet with a pride of lions constantly on the prowl, each mouthful of grass might be it's last. But somehow zebras don't think much about lions.
Put yourself in the zebra's shoes (or hooves) for a minute. Imagine that every time you went to the local Whole Foods you had to keep a lookout for a stealthy and ferocious predator, silently preparing to shred you to pieces. And guess what? He's at Starbucks too! And maybe even waiting for you in the handicapped stall at the food court! Do you think you would be a happy person?
Worrying interferes with your ability to be happy. Worry is different from fear. Fear is a response to specific present threat. Worry is more abstract. It is concern for events that might happen in the future, which may be unpredictable and which you may lack control over. Worry is quite difficult to accomplish when, like a zebra, you lack much of the neural architecture to project yourself into the future.
Unfortunately, worrying activates the body's stress response in much the same way as fear. This is problematic because the stress system evolved to deal with occasional threats, particularly the kind you have to physically run away from. These days most people have little physical threat to actually fear, but we spend a lot of time worrying. This results in a stress response that is always on, and that eventually leads to health problems.
In some sense the PFC is designed to worry. Because worry is a projection of yourself into the future, it is not something that can exist when you focus on the present. Zebras, like pretty much all animals, are forced to live in the present. Zebras don't get ulcers because they don't spend their time paying attention to things in the future over which they have no control. When you find yourself focusing on possible events in the future that you can't control, do your best zebra impression and shift your focus to the present.