It is a punch to the gut. That sudden, nauseating realization that the person who just walked out of your life was actually the "one," or at least someone you weren't ready to lose. Most of us first heard this sentiment through Mike Rosenberg—better known as Passenger—in his 2012 folk-rock hit "Let Her Go." The lyrics "only know you love her when you let it go" struck a nerve globally, topping charts in over 20 countries. Why? Because it isn't just a catchy line. It is a documented psychological phenomenon.
We are notoriously bad at valuing what we have while we have it.
The human brain is wired for novelty and survival, not necessarily for constant, conscious gratitude. When someone is always there, they become part of the furniture of our lives. You don't notice the oxygen in the room until the door seals shut and the levels start to drop. Then, suddenly, it’s the only thing that matters.
The Science of Why We Appreciate Too Late
Why does this happen? It’s not just because we’re "ungrateful" or "bad people." Psychology points toward a few specific glitches in our mental operating system. One of the biggest culprits is hedonic adaptation. This is the observed tendency of humans to quickly return to a relatively stable level of happiness despite major positive or negative events. When you first fall in love, every text message is a dopamine hit. Fast forward two years, and that same person’s presence is your "baseline." You stop seeing them as a gift and start seeing them as a given.
Then there is the fading affect bias. This is a psychological phenomenon where the memories of negative emotions fade faster than the memories of positive ones. When you are in the thick of a relationship, you might be hyper-focused on her annoying habits or the way you argue about the dishes. But the moment she is gone, those irritations evaporate. Your brain filters out the "noise" and leaves you with a highlight reel of her laugh, her support, and the way she made you feel safe.
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You aren't just missing her; you're missing a version of her that your brain has scrubbed clean.
The Scarcity Principle and Loss Aversion
In economics, there is a concept called scarcity. We value things more when they are in short supply. The same applies to human beings. When a partner is "available," their value stays at a market equilibrium in our minds. The moment they become "unavailable"—because they left or moved on—their perceived value skyrockets.
Daniel Kahneman, a Nobel Prize winner and author of Thinking, Fast and Slow, famously explored loss aversion. His research suggests that the pain of losing something is twice as powerful as the joy of gaining it. The realization that you "only know you love her when you let it go" is essentially loss aversion in its most raw, emotional form. The "gain" of her love was something you grew used to, but the "loss" of it creates a psychological deficit that feels unbearable.
Realities of the Passenger Effect
Passenger wrote that song in a dressing room at a regional gig in Australia. He was going through a breakup and felt that specific, stinging regret. It resonated because it’s a universal script. But we have to be careful with the narrative. Sometimes, "letting go" is the only reason we think we love them.
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Is it true love, or is it just the ego reacting to rejection?
Often, people mistake the panic of abandonment for the depth of their affection. If you didn’t treat her like you loved her when she was there, did you actually love her, or do you just hate losing? It’s a hard question to answer. Real expert-level emotional intelligence requires distinguishing between valuing a person and regretting a change in circumstances.
The Role of Retrospective Interference
Our memories are not video recordings. They are reconstructions. Every time you think about her after the breakup, you are rewriting the story. This is called retrospective interference. You start to project your current feelings of loneliness back onto the relationship, convincing yourself it was perfect.
This is why people get stuck in "on-again, off-again" cycles. They let go, realize they "love" her, get back together, and then—within three weeks—the hedonic adaptation kicks back in. The annoying habits return. The "love" fades because the "loss" is no longer a threat. It’s a toxic loop driven by a misunderstanding of how our brains process stability versus instability.
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Breaking the Cycle: Actionable Steps to Value What You Have
If you find yourself nodding along to these lyrics, you're likely in one of two camps: you’ve already let go and are hurting, or you’re afraid you’re taking someone for granted right now.
If you are currently in a relationship:
- Practice active "Mental Subtraction." This is a technique where you spent five minutes imagining your life if you had never met your partner. Don't just think about it—visualize the empty space in your bed, the silence in the kitchen, and the absence of their specific support. Research shows this boosts relationship satisfaction more than just "counting your blessings."
- Disrupt the routine. Hedonic adaptation thrives on "the same old thing." Change your environment. Travel. Try a new hobby together. Force your brain to see them in a new light so they don't blend into the background.
- Check your "Bids for Connection." Dr. John Gottman, a leading researcher on marriage, talks about "bids." These are small attempts your partner makes to get your attention. If she points at a bird or mentions a news story, she’s making a bid. Turning toward these bids is how you maintain the "love" without needing the "loss" to wake you up.
If you’ve already let her go:
- Audit your memories. When you feel that wave of "I love her" hit, ask yourself: "Am I remembering the person, or am I reacting to the silence?" Write down the reasons the relationship ended. Be brutally honest.
- Accept the lesson, not the person. Sometimes, the purpose of a relationship is to teach you how to be a better partner for the next person. You might only know you loved her when you let her go, but that doesn't always mean you should go back. It might mean you finally learned how to value someone.
- Avoid "Cyber-Stalking." Checking her Instagram or LinkedIn only fuels the scarcity principle. It keeps her "present but unavailable," which is the worst possible state for your brain to heal.
The "Passenger" sentiment is a warning, not just a sad song. It’s a call to be more present in the mundane moments so that you don't have to wait for the catastrophe of a breakup to realize what you had. Love is a verb, and if you aren't "doing" it daily, you’re eventually going to be "feeling" the lack of it.
Start by looking at the person sitting across from you today. Don't wait for them to become a memory before you decide they are worth the effort.