Beware big (and small) consultancies that promise *quick* **and** *lasting* change. The only legitimate reason to hire a consultant is to bring your organization into a position where you don't need them anymore.
And don't forget that it is you that will have to do all the hard work during the transformation and live with the results.
A book everyone who thinks of hiring a consultant should read first:
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I thought that consultants were hired to give management a way to lend an air of credibility to their own ideas, and to have someone to blame when things go wrong.
@Pat
Yes, unrealistic expectations and pressure from shareholders, lack of knowledge, and distrust in the people that work for them are big factors why managers hire consultants. The book expands in detail on that.
It is not all the consultancy's fault. They just provide a service for which there is demand.