How do you actually know when a side project is dead versus just stuck?

Dragging a dead project along for months just because you've already put so much time into it is a terrible feeling. I've been there you know deep down after month two that the idea has no traction but you keep writing code every night just to avoid admitting it failed.

Deleting that repository hits hard because it feels like throwing away all those late nights.

Looking back what was the exact sign that made you finally kill your project instead of pushing through?