Running with a bad idea?

On this site and beyond, I've read about some amazing ideas and projects that people have built.

These founders must have thought, "hey, this is a great idea!" and run with it.

But I'm sure that you, like me, have come up with many other ideas that are less good.

These ideas are the "it might work" ideas, the ones you write down but never circle back to.

But do we really know that these are bad ideas without testing them?

My question to the IH community is, has anyone had experience building what they thought was a less than great idea?

Did it turn out better than expected in the end? Did it surprise you? What did you learn?

Should we be building everything we think of, just to see if it works? Or should we let bad ideas stay in our notebooks...