Oman Air 787

"Head-to-head, my side." When you see a dot in the sky coming at you, hold very still and see if it is moving in the windscreen.

With practice, you can tell if the other aircraft will pass in front, or behind. Left or right.

Another aircraft, whose relative position doesn't change — is going to hit you.

Just like a car approaching your crossroad. At least, in aviation, we are at different altitudes. Or are we?