To understand someone, don't ask who they are. Wait for their situation to change, and see what they give up first.
This isn't a new invention. 2,300 years ago, a Chinese book called the Lüshi Chunqiu (Master Lü's Spring and Autumn Annals) boiled it down to eight sentences, each aimed at one kind of situation.
In short: what you watch is not his attitude but his trade-offs.
The originals are in classical Chinese, eight characters each. For each one below: first the line itself (translated literally), then plain talk, then a concrete picture.
The first six look at what he wants when he's on top; the last two look at what he holds onto when he's down. See both ends and you pretty much know the person.
By the way, the same chapter has six more lines about deliberately creating a situation to test someone (make him happy, make him angry, make him afraid, and see if he stays steady). Those go a step further and are more likely to hurt people, so we won't go into them here.
The last one is the easiest to forget: how you treat old friends when things go well is also being watched.
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