Out of such groups one is miserable (5)
I believe the answer is:
sorts
'out of such groups' is the definition.
The answer and definition can be both related to thinking as well as being plural nouns.
Perhaps there's an association between them I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for sorts that I've seen before include "Out of this is unhappy" , "Orders" , "Types" , "Systematically arranges" , "classes" .)