How can the fear be treated if it's causing a real problem in someone's life? More especifically the fear of stressful situations causing incapability

Yes.. There are lots of ways to treat the fear or anxiety about situations, from talk therapy, meditation, exercise, diet modifications, relaxation techniques, behavior modification, group therapy, hypnosis, acupuncture to medication, often a combination of multiple methods is required. Contact your doctor to taylor a plan that is specific to you and your needs.
PsychT/Stress mgmnt. Psychotherapy helps with identifying stressful situations; help rank situation from least stressful to the most stressful and work your way up. Look at the patterns in which you're responding to stress. Learning to identify things you can control and letting go things you cannot will help you with anxiety. Consider medication if anxiety becomes overwhelming. Relaxation, deep breathing, self-care.
CBT for some works. In contrast to other forms of psychotherapy, cognitive therapy is usually more focused on the present, more time-limited, and more problem-solving oriented. In addition, patients learn specific skills that they can use for the rest of their lives. These skills involve identifying distorted thinking, modifying beliefs, relating to others in different ways, and changing behaviors.