crtl + z

When drawing in real life I reach out for some sort of Crtl+z, I scream out "I wish there was a crtl+z button in real life!!!" my bro's all like "I know what you mean.."
One day I actually kept pressing crtl+z on my keyboard and nothing happened to my drawing, I must've been half asleep or something to realize the fact that I wasn't using my pc ._.''