I totally do not agree with the "balls" part. Yes, you do have to push your comfort level, but it is a skill progression that happens in benign situations. You then ramp up a bit to test confidence.
My domain has been kayaking - in all forms - training under several national team coaches, guiding on big, scary rivers in EurAsia and Patagonia, cake guiding gigs on rivers like the Rogue, Middle Fork of the Salmon, PSIA D-Team level in instruction, etc.
What you will find.... those athletes that are seemingly trying to kill themselves are really taking very calculated risks. They have honed the basics with endless hours of drills until the movements are like breathing in their sleep. They don't do drills until they get them right. They do drills until they can't do them wrong. A few will not have the skill. They will be "durable". That is not sustainable.
As I say in both ski and paddlesports instruction to those who express fear (rarely verbally - but through body language), "Skill acquisition is the antidote for fear". We then change venues to a situation that is more visually benign, and get back to working on basics. I never put my students in objective danger. However the venue may be visually challenging.
With quickness, it comes down to basics - efficiency. On skis, if I have to do one minute weight shift to make my skis do what I want, instead of three massive weight shifts and corrections, I have all the time in the world. On the river we work on two things: 1. What I term "elegent boat placement". You want to thoughtfully line up your next move, so you are ideally situated to nail it. 2. Efficiency in boat handling. I will take a more advanced student to gentle moving water (where they are pissing and moaning that they are more advanced than this), where we can do a ferry. OK, it takes them three strokes to accomplish the move. Now let's hone that to one stroke. No let's hone it to zero strokes, just using the boat's speed and angle to accomplish the move. Same in skiing. We may go to a very flat green run to do edging drills at 3mph (where they are pissing and moaning that they are more advanced than this). They fall over. Then learning begins.
All of this boils down to one of my other philosophies, "Patterns of grace / moments of pressure": you drill patterns of grace in benign situations, until your body only knows one way to respond. Then, when the shit hits the fan, your body responds in the most optimally efficient pattern possible.
In most cases, unless you are on the podium at national events, strength is not a player - unless it is to compensate for shitty technique. Technique, and the range of motion to put your body in a position that optimizes how your equipment is designed to be used, will consistently win. Their may be anomalies, but they are not consistent. Not sustainable.
As performance physiologist Michael Gervais says, "You can train your mind, your body, and your craft. That is all that you have."