@Orwellia
if you are the root user, everything you type is definitive even if it is to make you computer explode.

If you are a regular user, commands that would affect the system will issue some kind of "access denied".
The only damage you can do is on the files you have in your home directory

"rm -rf /" as root erase your whole drive

"rm -rf /" as a regular user tell you that you cannot do this!