Good read by Chris Dixon:
Suppose you have an idea for a startup, and then do some research only to discover there are already similar products on the market. You become disheartened and wonder if you should abandon your idea.
In fact, the existence of competing products is a meaningful signal, but not necessarily a negative one.
3) That other people tried your idea without success could imply it’s a bad idea or simply that the timing or execution was wrong. Distinguishing between these cases is hard and where you should apply serious thought.