How do you decide when a side project is worth continuing or time to quit?

I’ve worked on a small side project on and off for about eight months. Some weeks I’m excited about it, and other weeks I wonder if I’m just refusing to let it go because of the time I’ve already put in.

Last month I set a simple rule: if I couldn’t get even five people to try it, I’d stop. I managed to get three, and two of them gave me useful feedback. I’m still not sure if that means I should keep going or if I’m just reading a weak signal as a good one.

It made me wonder if “don’t quit too early” and “don’t hold on too long” are both true, and how anyone knows which one applies.

How do you decide when a project deserves more time? Have you ever quit something and later regretted it, or kept going and wished you had stopped sooner?