The "5 Whys" is a cornerstone of Lean Six Sigma. Go to the website. They offer a free "5 Whys QTools" PDF download. While the title is different, the content is superior to most generic "Why Ask Why" files.
Most people ask "Why did this go wrong?" The PDF expansion suggests asking: This shifts blame from the person to the process. It is less confrontational and more productive in team settings.