Whim

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Whim people.
Whim people is a term that has been used to refer to people that are only interested, or only seem to be interested in things based on whims, or they're only able to converse about things based on whim. In this sense people can be divided by how able they are to talk about topics with the passage of time, with some apparently only being able to talk about things in the moment that they are interested, while others are able to do so even decades later --- obviously many are somewhere in between. I.e. there are people who have "moved on," "lost interest," when you reply to them about a topic hours, or days, or weeks, or months, or years later, and then people who can respond about a topic days or even decades later.
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Psychological shallowness