If 12 o'clock is in front of you then 6 o'clock is behind you. "Check Six" is a term fighter pilots use that means nothing more than "look behind you".
It's easy to fixate on what's in front of you because, hey, it's right there in front of your face! If you look behind you, you'll obviously be looking at where you've just come from, but your perspective will be different, so what you see will also be different. You'll be looking at something you've already seen, but you'll be seeing something new.
The banner at the top of this blog contains a photo that was taken at the end of a day of making beach images. I was walking away from the beach, toward our cabin. On a whim, I turned to look one more time at the beach scene behind me and saw the cyclist in silhouette; you see the result.
You obviously can't look over your shoulder all the time, but every now and then check six; you just might be pleasantly surprised.
Tide Rushes In
The Alibi Room
Frosted Window Panes