That just amounts to never cutting your losses & throwing good money (or time) after bad. The fact that it's a difficult decision with risks of being wrong eit

That just amounts to never cutting your losses & throwing good money (or time) after bad. The fact that it's a difficult decision with risks of being wrong either way is not a good reason to avoid making it. If you're going to choose perseverance it should be a reasoned choice, not the result of inaction due to uncertainty in the face of a difficult choice. Before "move fast & break things" became the slightly misguided mantra for SV the message was often wisdom, much more tempered by decades of startup culture, was "fail fast and move on". Most will fail. If the only thing you have left is vague hope and a willingness to work hard and very little else then it's best to put that optimism and work ethic into a course of action where the preponderance of evidence doesn't already point towards failure. Of course it's a balance, but don't be afraid of making a decision just because it isn't an easy one to make.