What I learned today is to carefully read messages in the Linux terminal

Just recently I tested a couple of email clients on my Ubuntu machine, one of which was Evolution - the Gnome email client. Since Evolution doesn't allow me to implement CSS/HTML code into the email editor, I decided to uninstall and purge the client and its related files in my Linux terminal. 

Later when I rebooted my system, Linux didn't start Gnome-Desktop and I got stuck in the terminal, almost causing me a heart attack. At this point I realized that something went wrong when I uninstalled Evolution and its related files. In order to fix this, I first tried the command

startx

which showed a GUI with an error page saying that something went wrong.  As it turned out, uninstalling Evolution also removed Gnome, or at least parts of it. As a consequence, I reinstalled ubuntu-desktop and rebooted the system by entering the commands

sudo apt-get install ubuntu-desktop
sudo reboot

which fixed the issue. After my system rebooted Ubuntu-Desktop worked again.

What this instance taught me is to carefully read the messages in the terminal, because the terminal shows you a list of files that will be removed and asks for confirmation. Nevertheless, I also think that Gnome and Evolution should be strictly separated from each other, or at least during uninstalling Evolution, in order to avoid this kind of incidence.