Don’t forget to leave a buffer for maintenance!” was what me, my superiors and colleagues always reminded one another when we were about to plan a Sprint. “How much of a buffer?” was always the followup question. The answers range from “I don’t know, figure it out”, to “a rule of thumb says X%”. For some reason, no matter which X we choose, we ended up being wrong. By the end of this Planning series, we’d know why. Hopefully we’d also know how to do it right. In order to get there, first we need to decompose everything we know about buffers and expectations.