Being too confident in one's e.g. abilities. It can lead to disappointment, or "arrogance". Perhaps because the society values modesty, this may not be a good thing. However, it's not up to society to decide in the end what you think!
I see this as the main reason why teachers treated overconfidence like a nuclear bomb: Here,
it's almost always better to know more than know less, study more than
study less, and get the marks instead of not. Hustle culture at bay,
making its way to school! However, humans are biologically wired to be
more careful when they feel they are losing something they already have
than when they are trying to get something they don't have yet. This is
the overconfidence problem.
Also, pride and completion of a high-mark question often leads to
sloppiness, especially in re-checking the paper.
It’s best to check every corner for traps. Read the question twice to
make sure the exam writer isn't a trickster.
Gaining is about ego and feeling good. Avoiding loss is about survival
and being careful. Carefulness beats ego every time in a high-stakes
exam.
This also disproves my principal’s point that people can get 1% better
each day compared to their previous self: If I start at 30% and study
for 300 days, she claims that I can exceed 100%, which is impossible
motivational propaganda to prevent most unknowing students from feeling
like their efforts are a waste. In fact, the change in raw marks in past paper
drills usually decreases as it increases, like reducing mistakes by 1%
each day (exponential decay of error), the mathematical functions are
completely different.
That's why I was a pessimist for a while: Expect nothing. Because really, things rarely go to plan, almost never "optimally"! And the disappointment hits... what a pity... It pities my soul when I think something will work, but it doesn't. In fact, I feared the Dunning-Kruger effect.
However, it is only recently that I realized that it's better to be more optimistic. Statistically speaking, I am a human, and I am thus bound to human psychology, which dictates stress levels decrease with higher levels of optimism, and motivation increases. However, there is still a conflict between the old and new versions of me. Thus it will take some time to fix.
Technology like AI can fail too! Even worse, some websites, or applications, or phone calls, may be scam or malware! Thus, don't be so overconfident that you become ignorant. I think this is the guideline from not on.