What is it and why is it important? Ok. Before I continue I want to ask you to get your mind out of the gutter, arousal does not always refer to sexual arousal. Like affect, which is the standard term psychology academics use to describe emotion, arousal is a term used to describe level of excitement - which may happen to be sexual in nature but more often than not simply relates to attentiveness or lack thereof....
A heuristic is another way of saying rule-of-thumb. It’s a thing you refer to when making a decision when fully considering the situation you’re in (from first principles) would be too time-consuming, expensive or about which you simply do not have trusted skills available. The availability heuristic is what happens when you rely on an immediate example of something when considering a topic. The flaw here is that the immediate example you’re thinking about may in fact have nothing to do with the topic at all....