[<< wikibooks] Free Knowledge Culture Calendar/July 8
1. Make each program do one thing well. ...
2. Expect the output of every program to become the input to another,
...

Today in 1978 Doug McIlroy first published a version of the Unix philosophy in The Bell System Technical Journal.
Following these principles facilitates the chaotic remote collaboration that is vital for the success of open source development, since even complex systems are preferably built in manageable parts.