There are many skills that can be expressed in the field of auto mechanics as a variety of automobile makes and types exist. In repairing cars, your role may be to diagnose the problem accurately and quickly. Your job may involve the repair of a specific part or the replacement of one or more parts as assemblies. Basic vehicle maintenance is a fundamental part of a mechanic's work in modern industrialized countries while in others they are only consulted when a vehicle is already showing signs of malfunction. Preventive maintenance is also a fundamental part of a mechanic's job, but this is not possible in the case of vehicles that are not regularly maintained by a mechanic. One misunderstood aspect of preventive maintenance is scheduled replacement of various parts, which occurs before failure to avoid far more expensive damage. Because this means that parts are replaced before any problem is observed, many vehicle owners will not understand why the expense is necessary.