Reelin' and ROCin', Receiver Operating Characteristic by David Lettier

Imagine standing by a murky stream. You notice objects floating passed you. Pulling out your notebook, you write down for each object how confident you are that it is a fish (between 0.0 and 1.0). Not all are fish with some pieces being trash. Downstream, your friend scoops up each object and writes down what it actually is.