Means not to formulate an opinion about them based on the known knowns of the said person or what they choose to disclose about themselves, since there is more to them than the impression their certain actions, words would imply. I dunno.
To elaborate in the words of the astute Rumsfeld :
"As we know,
There are known knowns.
There are things we know we know.
We also know
There are known unknowns.
That is to say
We know there are some things
We do not know.
But there are also unknown unknowns,
The ones we don't know
We don't know. "
I think majority , infact 99% of the people make a judgement on very little information AND knowledge. Infact, majority of the time, they judge others negatively while they do the EXACT same thing themselves. And also, some people state their judgements in a manner that is very inappropriate and embarrassing for the other person. I'd rather not embarrass someone, but to each his own.
You should only judge a person if you make every effort in the world to strive perfection and if you actually have an intellectual brain and a heart that can do justice.