I have occasionally (and very recreationally) raced on track days. I do not know kart racing well, but even in a relatively slow (15 year old BMW) car, it's incredibly scary to race towards a brick wall at ~180 km/h and only brake at the last moment.
So I think that 10% is a lot of skill and dedication, but also a sort of numbing to that fear.
I've done a lot of track days. You realise how big the skill gap is between an average person like me and a proper fast driver.
I've occasionally gone into a corner way faster than I should with my abilities, frightened myself, but the car has stuck to the track. It made the corner. I couldn't do this intentionally, even knowing that I can throw it into the corner x mph faster than I'm comfortable with and I will come out the other end pointing in the right direction, I still can't do it.
Then you realise that if I gave my car to a racing driver, he would drive it like that in every corner of every lap. Because he has to, because if he doesn't he's giving away time.
It blows my mind.
My limit for how fast I can drive a car is so much lower than even an average road cars physical limits.
Agreed, I'm much more at the limit of the kart for every corner. If i crash, its not much $ out of my pocket. The value of the car is always at the back of my head when doing track days - even when its relatively "cheap", and thus I am slower. It take me much much longer to get up to the limit on the car :/
So I think that 10% is a lot of skill and dedication, but also a sort of numbing to that fear.