This paper spells out the following line of thought: (A) How much we care about various things is in constant flux, even as the world remains as it was. Internal affective shifts due to changes in mood, arousal-states or even hunger cause us to be more or less concerned about something. (B) Further, there often isn't any fact of the matter about how much we ought to care about something. As I argue, it isn't the case that there are prudential or moral norms that fix how worried we should be about every state of affairs in the world. (C) And this suggests that what we should do, both prudentially and morally, is often subject to our affective shifts, at least if how much we (permissibly) care about something is an important element of practical reasoning.
See for instance Harry Frankfurt“The Importance of What We Care About” in The Importance of What We Care About(Cambridge: Cambridge University Press 1988) and The Reasons of Love (Princeton: Princeton University Press 2006) Susan Wolf Meaning in Life and Why it Matters (Princeton: Princeton University Press 2010) ch. 1 and my “Wealth Disability and Happiness” Philosophy & Public Affairs 39 (2011) 177–206. As I will use “caring” caring about something involves certain desires but has deeper dimensions as well especially seeing something as important which I don’t believe can be reduced merely to what we want.