This is a very interesting post. Psychology of skydiving; one thing I never could do was mentally count on my first few freefalls. You know, arch-thousand, one-thousand, two-thousand, etc. After studying the physics involved in potential and kinetic energy exchange along with some basic rectilinear motion problems, I could accurately judge distance traveled without counting.
Altitude awareness as everyone has mentioned here on this thread is logically sound to longevity. When on AFF training, where you look at the ground and check your altimeter numerous times. This training is actually much more conducive to altitude awareness then counting manually during your first five or ten second delay literally scared out of your wits. At least I remember I was.
The more you jump, of course, the more comfortable you will be with your surroundings. So currency, is very important "Man Small, Why Fall, Skies Call, That's All"