I mean, the infamous "UNIX way" of "do one thing, do it well" (something we nearly lost with popularity of "do everything in a manner incompatible with how others do it" approach in too many modern systems), when complex behavior was frequently achieved through the modularity of smaller programs communicating through well-defined interfaces.

Heck, microkernels are all about this, and their ideas haven't grew out of nowhere. And HURD (even though it was never finished) is quarter a century old already.