Repair Disk Permissions

Doing something called Repair Disk Permissions is the scratch, it seems, to many itches under Mac OS X (example from Apple along with a detailed explanation of what it does and an introduction to file permissions), so it’s something I do, using the Disk Utility application, every so often.

What I’ve never understood is why I have to run this multiple times for all “file permissions issues” to be resolved. It seems that the first time through some permissions are repaired, then the next time through there are some additional ones repaired, and so on, until finally, after three or four times, everything gets addressed.

How come?