The ideas themselves are just stubs that could be built into a business, not plans or details. In face, I would argue that by themselves, they're worthless. There are lots of good ideas out there, which go nowhere. For example, "website marketplace to allow people to list their apartments like hotels," does not mean you invented airBnB. It's just an idea, floating around. Even if you wrote it down, it's not clear that I'm the right person to do it, or that I would have/could have had the same outcome.
When I look back on them, most of them are easily shot down as horrible upon even a small amount of reflection: too expensive to acquire customers, industry I know nothing about, too much of a marketing gimmick with little behind it.
A few others ideas are shot down by a google search revealing that I'm several years behind and 1% in my thinking vs other people who entered the space a long time ago. My 'innovation' is inevitably minimal.
Sometimes, the idea seems really exciting at the time, and then when looking back at it, it no longer does. Maybe the prize isn't big enough, or you just couldn't imagine yourself getting up every day and trying to build it.
Then, there are a few that get a bit further. I've spoken to people in industry or mocked up website -- even customers. And, often you learn things that you don't expect, usually that there's a reason why this doesn't exist. An industry structure you didn't fully understand or different motivations for decision makers.
And then, well, there's the exciting ones. The ones that make you leave your job, your safety and go for it. It's good to know that there are a lot of those too. And, even when the idea becomes a business and inevitably morphs and changes, that initial genesis and spark, is always a bit amazing.