"If you are the only user on your Linux box, you may be
wondering what's the point of having all these permissions (or lack
thereof) that restrict your access to your very own penguin OS.
However, before pulling your hair off, you must keep in mind Linux
is designed to be a multi-user environment. In an environment with
more than one user, it is crucial to have a secure system for
deciding which files are yours and who can fiddle with them.
"Even if you're the only user on an ordinary desktop system,
file permissions help keep your important files safe, both from
outsiders and your own mistakes.
"Understanding file ownership
Every file on your Linux system, including directories, is owned by
a specific user and group. Therefore, file permissions are defined
separately for users, groups, and others."