I do a lot of Civil 3D training and technical support. I see, over and over, people picking a Civil 3D object, running a command from the ribbon, and not realizing that the Civil 3D object is still selected after they get out of the command. If the next thing they do is select something for Erase, the Civil 3D object will be erased, too. You do that and you're gonna have a bad day.
There are a few ways to avoid this error:
1. Set RIBBONSELECTMODE to 0. This AutoCAD system variable will cause AutoCAD to de-select a Civil 3D object that was edited using a command run from a context-sensitive Ribbon tab. This is the safest way to work, but might cause you to need to select your object multiple times. That's better than accidentally erasing it, but seconds add up.
2. Start commands from the right-click Shortcut menu. Accessing commands here does not cause persistent selection.
3. Use the Esc key. Once you get used to having to Esc after every Ribbon command, it will become automatic...except for that one time you forget.