In 2014, the Office of the Special Inspector General for Afghanistan Reconstruction ("SIGAR") undertook a project with the aim of learning from mistakes made in Afghanistan post 9/11. SIGAR has produced several reports in recent years on this topic, which were purportedly based on interviews with a variety of people (most speaking with the promise of anonymity) with first-hand experience of the subject.
However, it transpires that those reports were not as full and frank as they may have been.
Over almost four years and two court actions, The Washington Post has gained access to a large amount of the information ingathered by SIGAR and it paints an interesting picture of how successive administrations have sought to mislead the public.
There's loads of articles out there about this, but the link below is a decent high-level guide. If there is one quote that sums most of the others up it's "it was sad to see so many people behave so stupidly".