In neither of my start-ups did I come up with the “idea”. I did come up with the idea of how to execute the idea and bring it to life, however. Without that, there is nothing.
In my first start-up, the original technology had been developed as a $50,000 internal lab experiment. While the results were somewhat promising, no customers were willing to buy, and the project was non-core, so it was dropped. My contribution was seeing the market was going to grow rapidly, that buying the technology and putting it in its own company would unlock the value, and recruiting the initial team and capital (including the folks who had done the lab experiment). But the idea? Not mine. Not at all.
The second time, I built the original crappy wireframes in Powerpoint, half-copying the UI of another app that did something very different. I recruited the CTO and dev team, and raised almost all the capital. I provided the belief that the idea would be a true commercial business. But the idea itself? Not mine.