Despite an increasing catalog of experience, I am always surprised to find people who don't share the same pervasive familiarity with game mechanics that I do. I've tended to play and discuss games with other people who play and discuss games. Most of the assumptions that are safe enough in such a circle aren't as universal as we think.
When was the last time that you had to explain that jumping on enemies kills them? Or that you could go down pipes? Let alone what it means to circle strafe.