It's my turn on stage. Smiling broadly I walk over to the stage with my computer. I worked hard on my slide-deck and pre-loaded all the webpages just in case the Internet connectivity failed. Connect my computer with a VGA cable to the projector and realize that I need to mirror my screen. So that the audience could see my computer screen on projector. That should be easy to do. So I open my computers display settings on Gnome control center and hunt for the 'mirror the screens' option. I can feel scores of eyes follow my every move. There is no option to mirror the display screens, I break into a cold sweat. I regret not saying a prayer to the demo gods.
Miracles happens, my fellow presenter Yang was my guardian angel. He had one trick up his shelve. He took the computer and typed this magic command into the terminal.
xrandr --output VGA1 --same-as LVDS1
That worked! I wipe the sweat and thank Yang profusely. Now it's show time.