Like many other things in life, it’s safer not to be too close to any boundaries (like a fish at the edge of a school in shark infested waters, or someone walking on a ledge 200 meters high with no safety net).
This from a website article about the dangers of using the DOS program FDISK. Simple typos in FDISK can cause it to begin formatting your hard drive, and disk recovery tools can only recover files where the directory information nodes pointing to those files are still intact. Since the FDISK format starts at the root directory and destroys the root directory information node first, you generally cannot recover files from the root directory once you’ve accidentally started formatting the drive. This is bad as it’s the files in the root directory that allow your computer to do things like boot up when you turn it on.
I like that the author pulls a general principle out of this technical mess. If you like safety then finding yourself on a boundary is a bad place to be. Political constituency, religious practice, medical diagnosis, restaurant seating, cellular phone coverage, etc. You’ll have a less eventful ride when you’re located smack in the middle of your group.
In software engineering this boundary principle is called the “special case” — the bump in the data that cannot be processed by the simple, elegant algorithm that works fine for the bulk of the data. Oh, special cases can still be processed, but only after attaching bells and whistles — inelegance — to your elegant algorithm. Something like 70% of the work of programming goes into dealing with special cases.