Consultant are usually persons who claim they already have big experience and knowledge in their subject/field. Their workscope is to CONs their client to provide all the information (confidential and non confidential) and then INSULTs the client by producing the final report containing all the information that their client just give (but in a nicely packaged and presented manner).

hence CON + INSULT = CONSULTANT

well that may not apply to all, but in certain field.... it happens.