> I'm having trouble thinking of when it's not clear. I phrased that badly. Past costs are always sunk. What's often not clear is whether the costs have yiel

> I'm having trouble thinking of when it's not clear. I phrased that badly. Past costs are always sunk. What's often not clear is whether the costs have yielded a positive return or a loss. If you bought bitcoin at $50K, and the price today is $30K, your investment has yielded a loss. If you bought Tesla at $100 and the price today is $700, your investment has yielded a profit. If you've trained 7 years for the 100m freestyle, and today you're ranked fifth in the world, your training investment has gotten you to fifth in the world. Beyond that, it's difficult to assess the value. What are your aims? What are your prospects? Let's say your aim is to win an Olympic medal. Should you train for another year in your quest to win an Olympic medal? If you train for another year, will you win an Olympic medal? The only certainty is that if you stop training, you won't win anything, and your investment has been in vain. Your costs are sunk with no return. It's that certainty of failure by quitting, vs the uncertain but non-zero prospects of winning if you carry on and invest more, that nudges you towards the possibility of sunken costs fallacy i.e. throwing good money or time after bad, even past the point of no return.