Research suggests humans don’t easily remember non-essentials or events that don’t hold significance for us. Ernest Hartmann, professor of psychiatry further explains that the reason we may forget can in part be attributed to the absence of, or low levels of the hormone norepinephrine (this supports memory) in the cerebral cortex when you’re dreaming. However, dreaming is the opposite of focused, intentional thinking and learning, hence dreams are likely more easily forgotten. Of course, there are dreams that will always stand out, you may even remember some vivid ones dating back several years.