In Casablanca, when Rick looks Ilsa straight in the eye and tells her, “We’ll always have Paris,” the idea of nostalgia was born in popular culture. These famous words meant a perfect past was gone, but a memory would linger like a diamond ring, sparkling and forever.

Of course, depictions of nostalgia go back even farther than 1942, perhaps all the way to Odysseus, who used the memory of family and home to power through a treacherous journey. After all, the word “nostalgia” comes from the Greek “nostos,” meaning a longing to return, and “algos,” being a general suffix denoting pain. Yet for as long as Odysseus’ journey was difficult, nostalgia has been viewed as a sort of mental illness, a disconnection from the real world, and a coping mechanism for the pathetic and melancholic.

Johannes Hofer, the Swiss travel writer who coined the term nostalgia in the late 17th century, thought that those experiencing nostalgia were little more than clinically depressed. About a decade later, scientists still didn’t know better and went searching for a “nostalgia bone,” thinking they could identify a physical cause for the sentimental feelings of days past. During the two World Wars, “nostalgia” remained a common medical diagnosis among wayward soldiers who tried to abandon the front. Even in Woody Allen’s Midnight in Paris, Paul — “the pedantic gentleman” — called nostalgia “the denial of a painful present” and “golden age thinking.”

Yet, contrary to what Johannes or Paul might think, nostalgia is less the denial of the painful present or a medical diagnosis of depression as it is a way to positively deal with our daily crises of existence.

From the Sartrean perspective, life is not about anything. Even worse, if you’re inclined towards Thomas Hobbes, life is “solitary, poor, nasty, brutish, and short.” So it is nostalgia that not only gets us through a difficult life, but also makes us feel meaningful and tied to a shared history. Think about your best memories. Almost always they involve someone else — a friend, a love, a family member — who contextualizes your life within a history bigger than yourself. When we’re lonely and thinking of the finiteness and smallness of our own lives, nostalgia gives us a wider lens to see how many people we’re connected with and how much we’ve experienced. Thus nostalgia is a way of feeling like we’ve made an impact on the world — nostalgia helps us matter.

Nostalgia reminds us how much we’ve accomplished, how deeply we’ve loved, how intensely we’ve lived.

Every so often, you might smell something that brings back a memory. Often the rest of the scene rushes back to you so quickly you’re nearly knocked out of breath, the memory shining vividly in your mind. Music tends to do this too, and entire days can come back to mind after hearing a single chord. Nostalgia and the senses that bring the past out of hiding are often so intense that the freshness of the memories conjured are akin to an amnesiac miraculously recalling an early-life event.

Young people, especially those in their 20s, are particularly prone to spontaneous nostalgia. In fact, Erica Hepper, a psychologist at the University of Surrey, found that nostalgia is highest among young adults. There’s a dip in these occurrences when one hits middle age — ostensibly when one is busier and neither particularly regretful of the past (as old people are) nor anticipatory of the future (as young people are) — and then another rise during old age when one becomes afraid of death and wistful of the past.

While nostalgia hits us like a train, and sometimes the memories of times past can chill us to the bone, it is almost always for the best. Although it can remind us that we’ve aged, that we no longer have what we once had, that life is no longer how it used to be, nostalgia also reminds us how much we’ve accomplished, how deeply we’ve loved, how intensely we’ve lived.

Perhaps most importantly, nostalgia is a way of fundamentally changing our past. Invariably, we reflect on experiences more fondly after the fact. The family vacation that was a miserable mélange of poor planning and bad weather is somehow remembered as “a fun family trip” two years later. That dreadfully awkward first date becomes “such a funny night,” and that exam we pulled an all-nighter torturously studying for morphs into “a great challenge that we embraced.” Thus we see the past with rose-colored glasses, and, in doing so, we make our lives feel more satisfying and positive.

Nostalgia is not a form of depression. In fact, it’s the polar opposite: It helps us feel better when we’re down.

It was Marcel Proust who said, “Remembrance of things past is not necessarily the remembrance of things as they were.” Yet he didn’t mean it to be disparaging. To remember the past affectionately is, in a way, to relive better times. Nostalgia may be seen less as a mental illness today, but it is still subtly derided. “Grow up,” they say. “Live in the present,” they say. Reality, though, is yours for the choosing.

Nostalgia brightens the corners of our sometimes dark and dull existences. It reminds us of starry nights with friends, youthful loves, and perfect evenings. So daydream, write about times past, and reflect often on your best experiences. Nostalgia is a beautiful thing, for it reminds us of good times had so we can look forward to the great ones to come.

This post was originally published at Thought Catalog and is reprinted here with permission.