In math you cannot know the sum before you know all the numbers to be added.
If you pre-suppose the sum is ten, then find the added numbers are 5, 3, 2, and 2, you are wrong. You cannot simply throw out one of the 2s to make yourself correct.
It is ridiculous in math yet we do it all the time in social situations.
We all have opinions and make generalizations whether it be about class, race, gender, age, whatever. We think we know the sum but very few make an attempt to find the individual digits to be added up.
Of course I know white/black people, I see them everywhere. I know because I watch, I pay attention. So goes perception.
I can look at a number 9, but if there is no context, I'll never know if the paper is upside down. Now if I can find 3+3+3 then I know it is in fact a 9.
What happens more often is people find 3+3 and then try to make up another 3, rather than accept that they might be wrong. Rarely does one consider the 6.
Most of us don't really want to know the answers, we only want to know if we are right.
The more I ponder this, the more I think I'm right, which helps prove my point.