I’d think that a good proportion, say 60-70% of my consulting projects over the years could be termed a success and the client was left in a better state than before we started. Sure, sometimes the monetary or other benefits don’t quite match the heights you showed in your beautifully crafted project summary to the board, but certainly a good proportion are delivered. The main reasons I’d say for project failure are:-Improperly scoped to begin with so no-one knew what would be delivered – often the case with the big government IT failures you see in the news-Projects that are “political” i.e. you come in the middle of a power struggle and consultants were only brought in as the sponsor couldn’t push it through internally so by paying a fortune for 3rd party advice they believe everyone else will have to listen to them. They invariably don’t.-Low client contact throughout the project, or “buy-in” to give it another term, so when you go they either can’t see the value of delivering what you say or can’t be bothered.To paint a VERY generalised assumption, I’d say reason 1 is most common in IT consulting, reason 2 in operations consulting, and reason 3 in strategy consulting.