Incurred sample reanalysis: failures in macromolecule analysis--insight into possible causes.

"Good people are good because they've come to wisdom through failure" - William Saroyan. Since the Crystal City III conference considerable effort has been spent defining what constitutes appropriate incurred sample reanalysis analysis. While what to do, such as the number of samples and acceptance criteria, is becoming generally recognized, it is important to step back and examine as a community what we are learning by this exercise.