I won't bog the post down with definitions from the FAA's "Fundamentals of Instruction" book, but in a nutshell the term "Primacy" refers to the concept of the things you learn FIRST are the things you remember most.
If you've ever been in the company of kids, they are a great example of Primacy. They remember EVERYTHING you say.
In aviation, you'll hear the term "bust" or "busted" used as a general expression to say "hey, you did something wrong". Examples are:
"Oh, he busted Class C airspace"
"You busted your visibility and cloud clearance minimums for this airspace"
...and the big one all budding CFI's will hear: "Don't bust primacy with new students"
I used the expression "busted primacy" in a way to infer that the client's previous instructor would teach concepts that did not exist in any aviation publications. In an effort to gain the admiration of his client, he would make up details "on the fly" that were unsubstantiated and had no way of being proven or not proven. I once overheard the instructor tell the student "You can NOT chop the power to idle or you will lose airflow over the elevator and it will stall!"
This is untrue and aerodynamically impossible. The student KNEW it, but he accepted what the CFI said because (as he later told me) "He's a CFI"
A simple example of Primacy being busted would be if during the early stages of flight training, an instructor were to say "We recover from a stall by ADDING FULL POWER!"
Now every time someone asks that student "So how do we recover from a stall?"
their answer will be "Full power!"
Opening the throttle fully might be a part of the recovery procedure, but a wing becomes unstalled when the angle of attack is reduced.
Just because someone holds their CFI certificate doesn't mean they're a GOOD
If you have the chance to fly with multiple instructors, you will definitely experience this.
As an instructor to a new client, I remind myself constantly to say as little as necessary, and the things that I must say, I must be concise and correct.
Jason does a phenomenal job of utilizing the concept of Primacy in his podcasts. He speaks slowly, he says only enough as necessary to make his points, and everything he says can be reinforced with an official publication or some plain old common sense.
On a sidenote, the client I made reference to did complete his first solo last Friday. The trick that did it was when I discovered that the previous instructor had performed NO power-idle simulated-emergency approach to land exercises with him (which made sense as it would defy his tenet that airplanes cannot approach to land with the power at idle lest they stall). We performed just four power-off landings, and each one was 100% better than the one before it. Once he acquired the confidence in the airplane gliding at idle-power, the solo was a BREEZE and his landings looked GREAT!
Let me know if I can be more specific. Thanks for asking Jeff!