The size and complexity of most projects mean they will take xx number of years to implement. Over the course of that time, the original aim & need for the item will no doubt change and the goal posts move. Adding onto that, most items are bespoke for the required role, often featuring new technology, so there are bound to be hiccups, teething problems or even complete re-designs required to overcome unforseen problems. Add to that far too many people sticking thier oar in, and trying to "save" money, it all add's up to a hideous mess that is over budget, over timescale, under performing and unreliable
