what did I do wrong?

[Geonz]

Part of my effective cycling course was practicing those "throw your butt back, brace your arms and slam on the brakes" stops (as well as looking back without weaving and the "lean right to turn left" to get around an obstacle move) in a big parking lot. Everybody in the class was an experienced rider, but it still didn't hurt to practice.
My bike's big rear end is not likely to go up into the air without extreme provocation, but it can fishtail if it's wet. My current rear brake is so noisy that it inspires me to hit the front first unless I'm in town and want to be sure to announce my presence at any intersection with a pig-like squeal. Interesting that SHeldon Brown says I need to use those back ones anyway.