i'm a rock, i put snow in my mouth so my breath doesn't show... PAK! you got hit! engaged from your left, you just didn't see that guy, coz you were just tooooo focusing on your front, you couldn't see your side...
that is why you need this - Optronics Rail Plastic Angle Use Scope ( BK )
with a small, transparent mirror fitted diagonally inside the plastic cube, the scene you will see, through this simple tool will be a combination of your front view, mixed with the view on either your left or right side (depending on the direction you twist the cube). you can simply mount it in front of holosights or scopes, and you can even choose to cover the front of this cube so you can view purely your left or right side. we found this simple tool especially useful in CQBs, when conditions do not allow you to expose your head for viewing
then next time when something approaches from your side, you'll strike first!
fits on regular 20mm rails, available in black and dark earth color