It's true! If you've got a 1 v 1 and you lose sight of the enemy in such a way you don't know exactly where they are, you're in deep trouble.
Let me clarify that. If you pull up and you know he's going "thataway" and is going to pass under your nose, or you're pulling lead, etc, you know where he is, so you've got mental "sight" of him.
What I mean is, when you're thinking "where the frak did he go?" you're in deep bantha poodoo. I was in a 190a5 and was engaged by a higher faster yak9u. We did a HO pass, he pulled hard to come around, but I basically didn't bother, I turned more to take a pot shot at a lower target then ran (I was alone, 10k, over an enemy field, with 12+ red planes on the deck and 1 yak at my alt. I took a potshot at a n1k2 and then headed for home as fast as I could.)
So after a bit the yak9u wants an easy kill. He chases me down. Did I mention VOX went out before this fight started? Yeah, no backup for me. As he gets closer and closer I figure i'm going to make this a hard kill for him. Normally a 190a5 is no match for a yak9u.
As he gets to 800 yards dead astern I pull a couple of scissors, always watching him behind me (or knowing mentally where he is) at all times. I force him ... well... not quite an overshoot, but I make him break one way while I go the other. We kind of get into this tree-hugging, terrain-following scissors/chase/overshoot/etc type of fight. It seemed to last forever. On some of the scissors he got a couple of pings, but with his weak weaponry I took no damage. The very last ping he landed on me took a flap off, but I wasn't using them anyways.
So, we're in this cycle towards the end of the fight where he comes in, I can break, break back, and get him to overshoot, and I'm actually confident I've got this guy completely. I'm actually seeing how I'll shoot him down, and have the plan.
Here's the point:
Then it happened. Somehow I lost sight of him, as he passed behind me. I got into a snap stall or some sort of small spin and had to correct. I thought we were crossing in opposite directions, but I look back, left, right, up, all around. I'm wondering if he ran away or crashed or something. NOPE!
My loss of sight almost cost me the fight. Turns out he was 600 behind me, then 400. Right about that time a friendly squaddie of mine dove in on him and made him break, so I was able to turn around. Yak9U came in again and I forced another overshoot or two, and I landed a 20mm in the cockpit as he passed in front of me. The Yak9u exploded.
Knowing where your enemy is is vital
I'd turned the fight around. I went from running, to annoyed, to actually certain I'd finish him off in short order. Then when I lost sight, game over. Without my squaddie there to scare the yak, at JUUUST the right time, I'd have been popped. Keep sight of your target! Or you become the target!
I just saw another thread and it really made me want to drive home to some of the "newer" folks that keeping an eye on the emeny really helps.
Having an 8-way hat thumb-button on your stick helps, plus another "look up" button so that you can look any direction, then any direction + "up" doubles your effectiveness as a pilot.