One of the more freeing things an investor can internalize is that the market doesn't know, and doesn't care, what you paid for anything you own. Said plainly like that, it sounds obvious. The implications get ignored constantly anyway. Your purchase price is a fact about your own history -- it isn't a fact about the stock. It has no bearing on the company's earnings, its competitive standing, the quality of its management, or the economic conditions it operates in. It matters to the stock's future no more than the price some previous owner happened to pay, which is to say it matters not at all.
And yet this irrelevant number exerts something close to gravitational pull over how most people actually invest. Positions get held long past the point their own analysis would justify, because selling below cost feels like conceding defeat -- even though the market keeps no record of any such defeat. Winners get sold the moment they claw back to breakeven, as if reaching the purchase price again were the finish line, when the actual goal -- the best available return going forward -- has nothing to do with what you originally paid. Money stays parked in deteriorating businesses because locking in a loss hurts more than the ongoing cost of holding a bad position, even though the market is entirely indifferent to which kind of pain you would rather feel.
There's a name for this: the sunk cost fallacy, the tendency to let money already spent, and gone, influence decisions about what to do next. Most people grasp this instinctively in other parts of life. Nobody thinks the cash already sunk into a failing project is a good reason to keep funding it. Nobody thinks two wasted years is a sound basis for staying in a bad relationship. Nobody finishes an unpleasant meal just because it's already been paid for -- or at least, they know they shouldn't. The investing version of the same logic, that a stock bought at a certain price shouldn't be held simply because today's price represents a loss, is understood just as clearly in the abstract and violated just as reliably in practice.
Part of the reason it persists is that an investment loss carries a psychological weight other sunk costs don't. It isn't just money that's gone -- it's a verdict on your judgment. Selling at a loss makes that verdict official. It leaves a permanent line in your trading history. It forces you to admit, in a way that simply holding on never does, that the original purchase was a mistake, or that continuing to hold it was, or that something changed that you should have seen coming and didn't. Each of those admissions stings. Doing nothing spares you from making any of them, at least for now.
There's a way out of this, and it's simpler than it sounds: treat every holding as a fresh decision rather than a legacy one. Ask, of each position, whether you would put this same amount of cash into it today if you were starting from scratch, with no history and no attachment to what you originally paid. Answer honestly. That question, and only that question, is the kind the market actually rewards, because it's forward-looking: where is capital best deployed from here? Your purchase price has no place in that calculation. It never did.