It comes from Parkinson’s Law by C. Northcoate Parkinson. He describes how a planning board will approve spending millions of dollars to build an atomic power plant but if you go to them to get approval to build a bike shed they will argue endlessly. The problem being that the atomic power plant is so large, complex, and difficult to understand that no one can really argue about how exactly it is done. On the other hand, everyone knows what goes into a building a bike shed and so everyone feels qualified to argue about the details.
For some reason, technical discussions seem to be particularly susceptible to bikeshedding.