History teaches us that many breakthroughs were happy accidents. Whether that's penicillin coming from Fleming neglecting to clean his laboratory before going on vacation or the team at Odeon trying a little side project that allowed people to communicate in real time as long as their message was 140 characters or less (which ultimately of course became Twitter), the unintended is often the transformational.
It's one of the underappreciated skills required by an innovator - they have to be able to convince lots of people to do things that might not be fully rational (invest in the company, join something that is likely to fail, try a product they've never seen before), and if you can't tell a good story it is just very hard to make that happen.
When we are looking at ideas, we really are thinking of three things. Are you doing something that seems consistent with the patterns of success? Are there reasons to believe you have or can access the right people to make it happen? Can we play a unique role in enabling success? We all have our rules of thumb, I suppose.
We've got some great big problems in our world. We have to figure out how to feed 10 billion people. Too many people can't access clean water, quality healthcare, and reasonable education. We have to figure out what to do about climate change, income inequality, and more. Innovators need to rise to the challenge!