Perhaps this is the crossover between Henry Spencer's observation about Unix ("Those who don't understand Unix are condemned to reinvent it, poorly.") and Green

Perhaps this is the crossover between Henry Spencer's observation about Unix ("Those who don't understand Unix are condemned to reinvent it, poorly.") and Greenspun's tenth rule ("Any sufficiently complicated C or Fortran program contains an ad-hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp."). The crossover is: "Any sufficiently complicated, real-world operating system contains an ad-hoc, informally-specified, perhaps buggy, implementation of half of Unix."