root permission denied

[Jonathan Michael Nowacki <jnowacki indiana edu>]

$ mkdir /usr/local/bin/update
mkdir: cannot create directory `/usr/local/bin/update': Permission denied

$whoami
root

drwxr-xr-x    4 root     root        10240 May 16 15:52 bin
drwxr-xr-x   18 root     root         1024 Jan 24 18:52 local
drwxr-xr-x   20 root     root         4096 May 28 13:11 usr

how is this possible, I thought root could do anything?