With startups, it's never over. That's a good thing and a bad thing! It's bad because you never really know when to quit, and there's always something else to do. It's good because there's always another chance.
Also, I've been thinking about this "solve your own problem" and "build the dream" kind of thinking for a while. I used to be a BIG supporter of this, but I'm not so sure any more. If you look at good investors, they have learned to separate what makes them excited from what the right investing decision is. I think startup founders should be a little more like this: sitting back dispassionately determining where to invest their time and energy. This is probably much more practical than trying to find the idea that makes them the most excited. Build the right thing, the right way, get traction -- you'll get excited. Trust me. Build something that turns you on, you could be in for a LONG slog of self-abuse. Startups are hard enough as it is -- for me, at least, tying my emotional self-worth closely into all that work is a really bad thing to do.
Odds are you will fail. Any amount of fanciful thinking is not going to change that. So, when it happens, it shouldn't be the end of the world. Instead, you should be emotionally in a position where you go, "Interesting! These 7 things worked. These 2 did not. What can I take from this and move forward? New idea? Change brands? Pivot? Etc." Being wrapped up in chasing "the one" only makes this kind of self-analysis extraordinarily more difficult. At least it does for me.