One way that the brain makes sure to remember the events that are important to us is through specialized chemicals called neurotransmitters, which, when released, help build stronger memories. One such neurotransmitter is dopamine. Dopamine is released in the brain when something surprisingly good happens, such as walking into class and finding a box of chocolates on your desk. When dopamine is released, it strengthens memories. It does so by tagging these memories when they are created in a way that makes these memories slowly strengthen over time. This means that just as memories for unimportant things start fading away, memories for important things grow stronger over time. In the end, memories for these surprisingly good events can have greater influence over our behavior, making it easier to use these memories to get the things we really want or need.
A similar process takes place when especially bad things happen, such as eating something that tastes terrible, encountering a spider, or other frightening events. This kind of fear learning depends on a specialized part of the brain, the amygdala, which works together with the hippocampus to strengthen memories.

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