When someone is on your back and your stomach down when someone is on your back, but they are back down when someone is mounted on top of you when someone is "knee on belly" when someone is on top in side control (think a chest to chest pin) AND they control the one arm near your face (which they should do) when your in someone's half guard AND they know how to position themselves on their side, in really close (where they should be) when your in someone's guard and they are using their arms to control either both your arms, or one arm and your head (like they should be) when somone has a "high guard" (the only guard i use) ANY position where a person properly controls you. i've grappled with thick "lab" goggles on many times. Unfortunately, extending your arms to, do anything, goes against a core principal of grappling in general. there are no absolutes. But in terms of self protection it is important to understand how to end up in mount (or some other top position) SO i can get to my feet to run.