Deep down, at the very root of our emotional reactivity, lies an addiction to the act/state of wanting itself. And as we saw earlier, 'wanting' means that we're actively wanting things to be different to how they are. This can manifest as any emotional reaction, anxiety, anger, depression, etc.
What we're really addicted to, however, is not the substance or experience itself. In this and in every other sort of addiction (drugs, alcohol, sex, gambling, shopping, etc.), we are addicted to particular body sensations – we're craving a physical feeling.
In order to support this root-level addiction of ours, we choose and create situations that produce those particular feelings. And just like all of the more well-known addictions, we soon build up a tolerance and need to up the ante (strength of reaction) just to get the same hit.
Addictions are notoriously hard to break! And this one is even more so, as it's hidden deep under all of the others. Neurochemically speaking, we are rewarded with a squirt of dopamine every time we experience the feeling of wanting.
In popular culture and media, dopamine is often portrayed as the main chemical of pleasure, but the current opinion in pharmacology is that dopamine instead confers motivational salience; in other words, dopamine signals the perceived motivational prominence (i.e., the desirability or aversiveness) of an outcome, which in turn propels the organism's behavior toward or away from achieving that outcome. [Wanting!] (Wikipedia)
When you find yourself reacting to something, focus on your physical sensations. Apart from the story/situation and the particular emotion, what does the raw body experience of wanting feel like in the moment? Sit with and investigate that.