"Of the most expensive software projects, about half will
eventually be canceled for being out of control. Many more are
canceled in subtle ways" (Survival Guide p. vii). The statistics are improving, but even in 2003 an
Oxford University/Computer Weekly survey concluded that only
16% of IT projects were considered successful. The Standish CHAOS report said that "the software success rate is 24 percent overall,
with numbers even lower for large projects, especially those in the
government sector". In short,
Slippage is a big problem.
"No-one is certain of the real cost of failed software projects, but in the US alone it is estimated to be upwards of $75bn a year in re-work costs and abandoned systems." (Computer Weekly).
According to The Software Development Edge (p.5) "most bad software results from less-than-inspired programming coupled with sloppy management". Maybe.
Once things start slipping it's hard to get them back on schedule - the situation tends to get worse rather than better. This may be because of the nature of the project or choice of procedures. Problems include