When installing FreeBSD, if you forget to assign your user to the wheel group, you wont be able to switch to the root user using the su command.
When running su, with a user that not in the wheel group, the following output is produced:
$ su su: Sorry
What’s worse, is since you cant switch to root, you wont be able to add the current user to the wheel group.
This post will show you an easy way to fix the problem.