I am not saying there is nothing wrong with the chances displayed, but as always I'd wager the overwhelming part of frustration is confirmation bias and human psychology. A 75% chance is not a guaranteed hit, yet it is treated that way. You wouldn't take odds like that in real life. Say there is a puddle on the road, you are wearing very nice shoes and you would guess that you are likely to be able to jump it, yet would most likely just step around it.
And with the amount of rolling in this game with varied chances the odds of having a bad streak every once in a while is high enough, and that is what sticks in your mind. Not the times four 75% hits connected in a row.
