Firstly I am not topper. or ranker.
but still i want to answer.
it happen with all. The master has failed more times than student has ever tried. It is in process.
i can share one incident at early stage i was looking for understanding some graph question. I watched every possible video on graph but still not able to understand. I kept this as it is.
after some month i realized it is from graph theory. funny isn't it ? which is totally new subject.
so some question are mixed from 1-2 subject you might don't know 2nd subject (probability
or Permutation & Combination or etc). once you complete them it will be very easy.
and one more imp point SOME QUESTION ARE INTENSIONALLY HARD so no one can solve in 3 hours that's why no one score 100%.
All the best :D