Moving grains to top shelf, observes that these constant changes are hard to manage (8,5)

'observes that these constant changes are hard to manage' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'moving grains to top shelf' is the wordplay.
'moving' becomes 'shifting' (similar in meaning).
'grains' becomes 'sand' (sand is made up of grains).
'to top' indicates taking the first letters (in a down clue, the first letter is top).
The initial letter of 'shelf' is 's'.
'shifting'+'sand'+'s'='SHIFTING SANDS'

Can you help me to learn more?