Idiotic Irritations

You know, there are some things that I am not meant to understand. Why I keep trying to figure said things out is beyond me. Maybe I'm just obsessively impulsive. For example, why is it that a person (say a mechanic) who is trained in a certain field of work is unable to perform the very service he is trained to do - thus meaning that the person who is not of the same field (my husband) must successfully do the job that the professional is unable to perform?