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.
This “tenth” rule is not really preceded by nine other rules, and its original date of publication is unknown. It’s a prescient warning about choosing the right rule for the job; a low-level language might not really be suitable for a sufficiently complicated task, and such a choice can in fact be self-defeating if it causes the programmer to reinvent higher-order abstractions imperfectly.