One thinks of them being upset when put aside (5)
I believe the answer is:
ideas
'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" .)