仅仅是好还不够

Plan 9 itself has never approached Unix in popularity, and was primarily a research tool. Plan 9 has been criticized as "seem[ing] to function mainly as a device for generating interesting papers on operating-systems research."^[8] Eric S. Raymond in his book The Art of Unix Programming speculates on Plan 9's lack of acceptance:

"Plan 9 failed simply because it fell short of being a compelling enough improvement on Unix to displace its ancestor. Compared to Plan 9, Unix creaks and clanks and has obvious rust spots, but it gets the job done well enough to hold its position. There is a lesson here for ambitious system architects: the most dangerous enemy of a better solution is an existing codebase that is just good enough."

--link from Wikipedia: Plan 9