Its almost impossible for an idea to be unique

I am not sure how many agree this. But it happened in my case. I thought of some, may be 4 ideas till now, which went much beyond just thinking almost up to complete market research.
The first one was more of a business rather than an innovation. After some research, came to know that the market is saturated. When I thought of this idea, almost assumed like nobody is doing it till now. One more idea was also discarded because of the same reason.
The third one was not as such seen in the industry now at full scale. But it is available in some form provided by some big player.
The fourth idea was kind of seemed to be unique. But its not. I have read in the news that there are couple of companies, which are implementing similar kind of idea.
It is the case with almost all the innovations, I have seen till now presented at various conferences and by various startups. But they are in form or the other available in the world. Probably the world has become so big that you could definitely find some people, who think like you. :) Probably this is the reason why the VCs don't sign NDAs when they hear ideas from startups. Its might so happen that, the idea was already there in his mind or somebody else's mind, the VC might have already heard from. Its been clearly said by a VC in HeadStart that don't be in a fool's paradise by thinking that the idea is not ever been thought by anybody else.