a) Few ideas are actually novel.
b) Someone else doing the same idea is validation of your idea.
c) The more time you spend actually developing your idea, the further ahead you will be of anyone else who has the same idea.
This is one thing that I had recently learned. Though it does not relive you from the pain (that the idea is not unique/novel), but when you keep on continuing with the idea, along the line you will find different ideas get attached to your project which may or may not be the same as how your competitor idea has progressed.
If you give it more thought you will realise that this outcome is generally because different people have different outlook towards the world. Along the line you will choose one scenario over other and solve it, and these choices will make a difference in the long run.
I have not reached that far, but this is how far I think I have understood.
I’ll definitely take that as a motivator, especially if I feel like I can build a better solution.