Recently, I've sat through some very impressive briefings lately on a very complicated project. The speakers have been knowledgeable and persuasive. The plans have been comprehensive. All possible downsides appear to have been anticipated. I'm confident that the client's project will be a success.
In the back of my mind, however, arose the thought that if we'd attended the briefings of the French General Staff in 1940, shortly before the German blitzkrieg turned the very idea of the Maginot Line defense into a strategist's joke, we would have also been impressed. No doubt the briefers were well-versed and eloquent. The visual aids were probably first-rate. All possible questions would seem to have been resolved.
How can we root out the possible flaws?
Re-examine the assumptions. The French thought one especially vulnerable area was blocked by an impenetrable forest. It wasn't. They had no effective response when their assumption proved to be false.
Review the danger of cumulative effect. Perfect storms occur. What happens if a series of small problems merges? Where is the final trench?
Make sure you have reserves. There is a famous moment in the battle of France when Churchill asks the French generals where is their strategic reserve and is told none exists.
Recognize, as the old saying goes, no plan survives contact with the enemy. The flexibility to shift with events is crucial. Planning is great but rigid plans can be senseless.
Overcommunicate. If you think you are overcommunicating with other units you are probably sharing information at an adequate level.
Finally, don't believe your own P.R. All joking aside, the French General Staff had some pretty capable officers in 1940. Beware of smugness and be especially wary of automatic deference to the top.
As a wise Italian diplomat once said, one of the most lethal gases is incense.