Why is there an infinite loop in the File System on a Mac? /Volumes/Macintosh HD/Volumes/Macintosh HD
/Volumes/&lt;startup> is simply a symlink, and there's no rules against where you can link.

$ ls -la /Volumes/Macintosh\ HD
lrwxr-xr-x  1 root  wheel     1B 22 Feb 15:40 /Volumes/Macintosh HD -&gt; /


It's not an actual infinite loop, only a loop of links; once followed, you're put back up the path.