The intricacies of the modern engine can be overwhelming.  It essentially converts chemical reactions into mechanical energy.  So many parts are involved and are all working together harmoniously.  If any of these parts start to fail the result can be costly.  Most engines these days are quite robust though and can take a lot of use for a long time as long as they're taken care of.  This means changing the oil of the vehicle on a consistent basis.  There are also many associated parts such as fuel injectors and sensors that keep these engine running smoothly.  Without knowledge of these parts it'd be very time consuming to diagnose a proper remedy.