Go at Google: Language Design in the Service of Software Engineering
From the article:"In 1984, a compilation of ps.c, the source to the Unix ps command, was observed to #include  37 times by the time all the preprocessing had been done. Even though the contents are discarded 36 times while doing so, most C implementations would open the file, read it, and scan it all 37 times. Without great cleverness, in fact, that behavior is required by the potentially complex macro semantics of the C preprocessor.""Great cleverness" apparently means "the ability to detect that a file has a standard 'include once' pattern and only process it once". It hardly seems like rocket science.