[randbox]

Pacman will happily break pacman and sudo without warning if the user requests updating openssl without upgrading the entire system. When updating a package it does not pull in all of the other packages which will break if not updated simultaneously.

[Jnr]

Indeed, pacman does not know which library versions are necessary for any particular app version. And almost all of the applications are dynamically linked.

Archlinux repo holds only a single latest version. There are some community maintained repos that contain older versions (and those can be easily fetched through downgrade utility).

When updating Archlinux, upgrade everything and then reboot. This way it should not break.