I dunno, but it just sorta makes sense. If my prime mode is then I prefer Thinking/Logic over Feeling/Ethics, and Extroversion over Introversion. Therefore my weakest would be the opposite judging (or sensing) function both in terms of the function and its direction (E vs I). So for me that would be which is where my dependency is.

It's just like an automobile engine, where if an engineer tunes it for best performance at high RPM, its performance will probably suck at low RPM, and vice versa. Or take your typical airliner with a high speed high altitude wing design. Great for long flights at high altitude, but the efficiency of the wing flat out sucks at low speeds and altitudes. A Boeing 777 will climb circles around a 747, but the 747 is a lot faster speed wise. The 747 design trades off lift for speed, and the 777 goes for lift instead.

So a brain tuned for will suck at


Sorry for no scientific explanation or link, but at least in the engineering "law of tradeoffs" no matter what you do to improve a design in one area, you're guaranteed to be screwing it up someplace else, and it still appears to hold true even for our brains.