The concept of Turn circle extension as visualized in this video. This made me realize two-circle fights are basically trying to perform a rendezvous maneuver in KSP.
Before this, I’ve lost flat-circle turnfights against P-47s in sim pulling as hard as I could constantly, which led to the infamous “yo-yo” effect where we closed in and then flew apart repeatedly.
Since this video, I’ve became concious of whether I’m in lag, pure or lead pursuit and started actively managing which state I am in depending on aspect and closure.
Another big Aha moment for me was learning about how gravity and lift (thus turn performance) interacts through the tactical egg.
These two things finally had me start winning dogfights in SB.
After these, I’ve had an “Aha!” moment connecting relative axis inputs and analogue results. Basically, I turned my rudder axis “relative” so pressing Q/E deflects the rudder without it resetting after I let go. Later I learnt this is how IL-2 rudder digital inputs function. I’m proud of independently discovering this - rudder has been saving me a lot in sim.
My recent “Aha!” moment was thanks to playing IL-2 and copy-pasting the camera controls I ended up using there back to warthunder because I missed “Free-look” being an option there, thus giving me these camera controls instead:

What this does (everything is relative) is that I can look around while retaining full mousejoy control.
WASD turns my head on axis.
13 makes me lean left/right
RMB raises head, tab RMB lowers head.
tab W/S gives me the ability to lean around cockpit frames/wing to look at targets when preparing a dive.
X recenters on gunsight.
Pressing 3d/1a makes me lean back and look around my tail better than freelook would allow.
And adding to this:
0% relative step makes for smooth axis inputs, 1% gives a considerable “deadzone.”
Nice part about these inputs is that I can control my pilot’s head without lifting my hand from the keyboard except for doing concurrent 1a for “lean left and look behind”.
Also on line of controls:
YAW/ROLL/PITCH sensitivity under movement also affects mousejoystick. If your nose wobbles weirdly and hitting shots feels impossible, set them to 100% These are wrongly named, they’re “filters” that create a delay on your inputs and cause laggy outcomes. Use the axis binds themselves to set non-linearity for actual control response curves.
Final added Aha moment:
“Climb!” isn’t just about having the ability to BnZ other planes. It’s also the ability to accelerate and maintain speed in high performance turns. Being able to drag an enemy down into a descending spiral turns a bunch of “US planes can’t turn” into “My P-51D5 just beat a Bf109K4”