One thinks of them being upset when put aside (5)

I believe the answer is:

ideas

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'one thinks' is the definition.
The definition and answer can be both related to thinking as well as being plural nouns.
Maybe you can see a link between them that I can't see?

'them being upset when put aside' is the wordplay.
'aside' can be anagrammed to 'IDEAS'.
Though, I am unsure how the anagram is indicated.

'of' is the link.

Can you help me to learn more?

(Other definitions for ideas that I've seen before include "Thoughts, concepts" , "plans" , "Fancies" , "Thoughts from Sadie" , "Notions, thoughts" .)

I've seen this clue in the Evening Standard.

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