Looking back it seems I use curiosity more for hours or days-long knowledge-gaining quests, e.g. immersing myself in a new academic field, whereas I use fear more when philosophizing on my own, especially about AI/FAI. Introspectively it seems that fear is more suited to examining my own thoughts or thoughts I identify with whereas curiosity is more suited to examining ideas that I don't already identify with or things in my environment. I suspect this is because people generally overestimate the worth of their own ideas while underestimating the worth of others' -- negative motivations reliably act as critical inductive biases to counterbalance systematic overconfidence in oneself, whereas positive motivations reliably act as charitable inductive biases to counterbalance systematic underconfidence in others. As you say, it's probable that others would have different cognitive quirks to balance and counterbalance.