In this case, the specific error was:
$ git pull
error: unable to unlink old 'sites/default/default.settings.php': Permission denied
I opened the sites directory and saw the following:
$ lll
  rwxr-xr-x  noxlady  staff  160 B    Tue Sep  4 13:34:39 2018  M?    all/
 r-xr-xr-x noxlady staff 192 B Tue Sep 4 13:40:49 2018 ✓  default/