Everyone has stress. It's foolish to speak of some people as "stressed" as if others go through life effortlessly. Being alive is stressful.
But you get to choose how you manage your stress. Often, people give in to it. They feel hopeless and defeated, which causes the heart to contract. You are literally hurting yourself when you "lose heart." Your muscles tighten, which stresses your whole body as if you had experienced an actual injury.
You can break the habit of stressing yourself by managing your expectations. If you expect your survival needs to be met without struggle, and expect people to get along without conflict, and expect to have fun all the time, the world will not meet your expectations. Something is wrong with the world, you may say. But blaming the world puts you in a powerless, hopeless position, and your heart contracts.
Stress just happens to you, in the popular opinion. It plops into your life from external sources, putting you at an unfair disadvantage against people you imagine to have no stress. This perspective overlooks the internal nature of stress, and your active participation in it. Such thinking leaves you powerless to do anything about your stress.
A stress habit can get reinforced by people who are trying to "help." Doctors and teachers may ask if you are "having stress," and you get the impression that you qualify for extra slack if you say "yes." Friends seem extra nice when you are "stressed," and they like you if you empathize with their stress. Identifying yourself as "stressed" has benefits that lure people. But it's not worth the cost. If people invite you to be stressed, just say no.
This is easier said than done. A shared identity grows among people who talk about how awful things are, and they regard you as a freak if you don't share this view. Such people come to think of themselves as heroic, and may accuse you of not doing your share if you're not in a frenzy as they are– even if you get more done than they do.
Animals face constant life-threatening survival challenges. Their bodies release cortisol when they perceive a threat. This is the chemical humans experience as stress. Cortisol creates the sensation that something must be done urgently. Animals have a limited repertoire of responses to that internal alarm. Humans complicate things with lots of extra neurons, so when our internal emergency alarm rings, we don't see a clear way to "do something."
Animals don't think something is wrong with the world, despite their survival challenges. Reptiles have thousands of offspring and most are eaten by predators. Lions fail to catch their prey 95% of the time and often go hungry. Male mammals don't get to have sex unless they fight their way up the status hierarchy, and female mammals are dominated by older females their whole lives. Of course animals don't conceptualize their stress, or project it into the future. They release it in the moment. But the next moment they confront a new stressor. They never give up, however. They just keep trying.
As long as you keep trying, your cortisol doesn't get the better of you. You evolved for action.
Humans have one kind of stress that animals don't have: awareness of our own mortality. Your brain reacts to this awareness as if it were a clear and present danger. Animals don't have enough neurons to terrify themselves with their own mental constructions. You can't escape from the knowledge that the world will spin merrily along without you some day. The thought triggers so much anxiety that people try to avoid it. They project the anxiety onto other things, like health care and finances. No amount of health care and finances will keep you alive forever, so you are better off accepting the fact that you are a vulnerable bit of protoplasm. It's an uncomfortable thought, but accepting it helps you stop stressing over what is wrong with the world. You cannot live forever, so you might as well make good use of the time you have.
If you find yourself stuck in the idea that something is wrong with the world, you're not alone. This idea is being taught as fact at most universities. But once you get your degree, you get to decide whether to invest your life in this paradigm. An alternative is presented in my book The Science of Positivity: Stop Negative Thought Patterns By Changing Your Brain Chemistry.