I've posted in the past about planning and preparation (for example, see "...plans are useless but planning is indispensable" or "Fools go aimlessly hither and thither..."). Over the years, a number of famous individuals have talked about the importance of planning and preparation too:
"It does not do to leave a live dragon out of your calculations, if you live near him." J.R.R. Tolkien
"By failing to prepare, you are preparing to fail." Benjamin Franklin
"Give me six hours to chop down a tree and I will spend the first four sharpening the axe." Abraham Lincoln
"If you don't know where you are going, you'll end up somewhere else." Yogi Berra
However, one of the most famous exampls of a failed plan comes from a video of a group of friends who were playing (I think) The World of Warcraft, a popular online fantasy role-playing computer game. The video was first posted on the fan site Warcraft Movies on May 11, 2005 and was later posted on YouTube the following November. The video has been copied and re-posted countless times (the most recent version with my link has over 16 million hits).
The video features a group of friends who meticulously plan a detailed battle for their next encounter. The character, Leeroy is away from his computer at the beginning of the video, and the plan is intended to help Leeroy obtain a piece of armor which everyone else seems to possess (so, the friends seem a little miffed with Leeroy anyway). At one point, the leader asks for a calculation on their chance of survival. However the survival probability is calculated, the answer is "32.33 repeating of course percent chance of survival." Once Leeroy returns, he rushes headlong into the battle, disrupting the whole plan. His friends follow him into the battle, and in the end, everyone dies!
It's a really funny video that illustrates what former President Dwight Eisenhower once said about combat, "Plans are useless but planning is indispensable." In other words, it's good to have a plan, but in the heat of the moment, some times those plans need to be changed.
I hate to disappoint you too much, but the video was apparently staged. Oh well - it's still quite amusing and it still makes a great point.