You get stressed out by being exposed to hardships, but you are not able to handle them. For instance, you may be having problems at work with your boss, coworkers, or your role has changed. Maybe you are having relationship problems with your parents, siblings, significant other, spouse, or children.Maybe you are spending too much and not making enough, and you are facing financial difficulties, maybe even on the brink of bankruptcy.
Whatever your hardships or stressors, they may overwhelm your capacity to deal with it. So your coping skills are not able to contain the stressors, then you become stressed-out. Another term for stressed-out is burnout. Symptoms of burnout include irritability, fatigue, insomnia, poor concentration, poor appetite, anxiety, depression, negativity, anhedonia (don't find pleasure in things), and social isolation. So it is important to be able to cope with your stressors before you become stressed-out.