Someone explaining to you why your idea wouldn’t work is vastly different than them explaining why it didn’t work.
The former is skepticism. It might be correct, but it’s theory. Even if it turns out to be true, running the experiment can still be worthwhile, to iterate towards success.
Giving you the benefit of prior experience, on the other hand, is a valuable gift. If someone tells you that they also tried the same idea and it failed, and why it failed, then you should listen. You’re basically getting the benefit of (at least) one experiment already run! You’re a step closer to success just by listening.
Importantly, the second person is also a more trustworthy source, simply because they actually tried the idea. That alone puts them on a different intellectual level than someone who simply decided from the armchair why they wouldn’t give it a shot.
Experiement, always!
The Opportunity Machine 