Many people talk about the high failure rate of projects, but rarely discuss where the numbers come from. I recently was working on a paper to discuss common issues surrounding 'lessons learned' and in order to back up the stats on failure rate, I had to track down where the fabled "more than 70% of projects fail" came from.
An American consulting company called Standish Group published 'The Chaos Report' (1995) which analysed project failure rates and failure modes.
As with many reports and documents, it is widely discussed and often disagreed with but many of the points made within it are quite valid and backed up by other (more academic) thinking.
My view? I'm not going to tell you what to think about it, but I would strongly recommend reading it so that you can make up your own mind, but at least know what you've been quoting.
You can find the report quite easily online - just use the key words 'chaos report'