Drivers at HPDE events go through alternating stages of discovery and repetition. Take the line for example: first, an instructor guides the driver on the correct line, or alternatively shows the driver the line. Then, the driver follows the line for a number of laps, with the goal to drive it consistently and without assistance.
The same cycle applies to driving techniques like smooth steering, getting on and off the brakes correctly, heel and toe. Once you know the theory and are able to execute any of these for the first time, you still need a good amount of practice. With practice you think less and less about the precise motions - your brain just issues a command and the rest of your body subconsciously knows how to execute it.
Discovery and repetition also apply to more fundamental concepts like smoothness, weight transfer and balance. Usually the concepts take longer to really be understood. Taking smoothness for example, a driver will be told to turn the steering wheel smoothly and get on the gas smoothly. Most novice drivers do not brake hard, so they would not be told to brake smoothly. It often takes an intermediate driver with a number of track days to really grasp smoothness as a concept and feel it in steering, throttle and braking, and to extrapolate that getting on and off curbs should be done as smoothly as possible - despite the fact that most classrooms don't include this as part of curriculum.
Now we can talk about confidence. Confidence is a skill that roots in concepts. Confidence is being able to turn 1 foot, 2 feet, 5 feet later than your normal turn in point. Granted, turning in later requires a line adjustment - and being able to vary the turn in point on the spot, such as when being passed later in a braking zone, requires a thorough understanding of the line theory. The first time you go way deep in a turn it can be discomforting. But with the knowledge that you made it the first time you can do it again and again, and with each subsequent attempt you worry less and less about staying on track. Then you can go deep in the corners you have never driven before and not freak out.
Confidence is tracking out to within 1 foot, 1/2 foot, then inches of the edge of the pavement. You have to know where the pavement ends and how wide your car is. These are bits you know subconsciously - you do not bust out a tape measure in turns!
Replace "edge of pavement" with "walls" and you have a whole new level of confidence to work toward.
Confidence is being able to vary your line slightly even at speed and knowing that you have a certain margin in your line that you will fit into, if the line variation does not quite produce the result you expect. Naturally, you have to know both your margins and how much of a line change a change in speed, steering angle or whatever should result in.
Confidence requires seat time to develop. Because confidence requires both knowledge and skills, it typically takes longer for a driver to become confident than simply skilled.
Note: aggression without knowledge is recklessness - an entirely different concept.