If the New England Patriots were on a software project their status report before Super Bowl XLII would have read something like 95% complete. The project team would have felt comfortable that the functionality was almost done and there wasn't much to worry about. The current status may have even led the project manager to abandon all risk mitigation plan for the functionality, after all, there wasn't much that could go wrong at this point.
As it turns out the 5% that was not accomplished by the Patriots was the most significant 5% of the project. The loss to the New York Giants means that the project goals were not accomplished. You can attribute the loss to many factors: Tom Brady's Footgate, The Giants' defense etc. The important lesson is that the 5% that was not accomplished killed the project goals.
So the next time you are sitting at a status reporting meeting or you read a status report that says something is 99% complete, don't fall asleep. Ask about the 1% that has not been completed, make sure it is not the most important 1%, the one that is likely to put the 100% of your project goals at risk. Personally, I don't use or allow people on my team to report percentage complete numbers. I ask to know what is done (and be clear about the definition of done) and what is outstanding.