Undoubtedly the longest running ‘urban myth’ in circulation within the general project management community, arising from US Defence based research from the early 1990s, that the Cost Performance Index (CPI) always stabilizes at the 20% completion and the final outcome will be within 10% of this value and usually worse. This myth has been extended by some authors to all projects in all industries; and I would suggest that this is demonstrably false in at least some circumstances.