Beyond Stupidity
I tried to install and configure Arch manually. After following the instructions on the wiki (basically, pacstrap and chroot), I planned to install certain graphical interface (Gnome on Xorg).
I learned that there are two package groups in Arch repository, namely "gnome" and "gnome-extra", respectively. After chroot'ing, I invoked the following command:
# pacman -S xorg gnome-extra
The installation was quite smooth. When I exited chroot jail and restarted, I saw a incomplete Gnome desktop environment. Even basic components like Terminal and Gedit were missing.
When I was trying hard to solve the problem, Mandy asked me: "Are you sure that 'gnome-extra' is a superset of 'gnome', i.e., that it contains everything from 'gnome'?"
Fortunately, I didn't have to re-install everything. Just boot into the installer, mount any necessary partitions, chroot, and install the core components of Gnome:
# pacman -S gnome
Note: Mandy is the heroine of this archived post: https://trisquel.info/en/forum/highly-embarrassing