Though varying in type and severity, fears (phobias) are a universal human condition. They are how the unconscious mind enables a too-stressed person to function. Their stress is caused by a psychological conflict or feared insight which disturbs the person's ability to function normally on the job or at home or in school.
For example, if an adult has problems in their marriage or another worry which they can't face, they may develop a fear of flying or of driving across bridges. A child may suddenly fear to sleep in their room and insist on sleeping downstairs on the sofa.
These phobias encapsulate the intolerable anxiety and enable functioning. Thus, the troubled person can engage in their normal activities so long as the feared object or activity is avoided. This is far quicker and easier than working through the emotional conflict in psychotherapy since, though inconvenient, most people can choose to avoid flying or driving over bridges, and sleeping on the sofa isn't a great hindrance for a child.
The unconscious mind is very powerful and one must respect its power.