It's not what you don't know that gets you…it's what you don't do scenario planning for.
Things people did not plan for that happened on February 28:
202 BC: The Han dynasty is established. People say it won't last. They're right. It only goes until 220 AD.
1525: Aztec king Cuauhtemoc is executed, establishing the Cuauhtemoc Rule: If you are an Aztec chief, never travel with a conquistador to a second location.
1953: James Watson and Francis Crick tell friends over cocktails that they have discovered the structure of DNA. The next morning they wake up and can't find the cocktail napkin, so they don't tell the rest of the world until April 2.
1954: The first color television sets using the revolutionary NTSC process are put up for sale, firmly establishing the 31-year-rule: any innovation that threatens to make life fun for kids will be adopted by my parents promptly 31 years after it is invented.
1998: The first U.S. flight of the RQ-4 Global Hawk, the first unmanned aerial vehicle certified to file its own flight plans and to fly regularly in U.S. civilian airspace. So if you've had a funny feeling that someone's been watching you for the last 15 years…
2009: Paul Harvey dies…and that's the rest of the story.
(Source: Wikipedia, except for humor content)