This is taken from a translation of the Visuddhimagga:

Suppose this person is sitting in a place with a dear, a neutral, and a hostile person, himself being the fourth; then bandits come to him and say 'Venerable sir, give us a bhikkhu' [Buddhist monk], and on being asked why, they answer 'So that we may kill him and use the blood of his throat as an offering', then if that bhikkhu thinks 'Let them take this one, or this one', he has not broken down the barriers. And also if he thinks 'Let them take me but not these three', he has not broken down the barriers either. Why? Because he seeks the harm of him whom he wishes to be taken and seeks the welfare of the other only. But it is when he does not see a single one among the four people to be given to the bandits and he directs his mind impartially towards himself and towards those three people that he has broken down the barriers.
Equanimity is a quality where you treat each being equal, and by this I mean equally well. An often-overlooked aspect of equanimity is portrayed here by means of drama - bandits threaten a monk to pick one of a company of four to be sacrificed.

Some spiritual traditions value "good" people over "bad" people and most people prefer this person over that person - so three varieties of people are present in this company of four besides the monk - a dear, a neutral and a hostile one, representing the range of feelings you could have for anyone. So, externalised is the whole range of the feeling range, and equanimity would require treating them equally. This goes beyond judgement.

But it goes farther than that. Many spiritual traditions value self-sacrifice, offering oneself up for the benefit of others. What this specific story highlights is that you (here the monk or spiritually aspiring person to identify with) are also completely included in the idea of equanimity. So, if you want to act from the ideal of equanimity you cannot offer yourself up as sacrifice for others, since you also are just the same feeling, sentient being as each other. You're no more and no less.

To honor this ideal you can neither judge others better or worse or more deserving or less deserving, and neither can you judge yourself in a similar way.

This concept is sometimes even counter-intuitive for many people, but I found it represented under another name as well - the "greater good of all." Many people would think that to mean a group distinct from themselves, even though "all" includes you, me and everyone. Or at least everyone in a given situation. If you honor the greater good of all in your intentions, everybody is served and you are never forgotten either. This balances your needs against everybody else's.

Oliver