This is very true. I happily discuss my ideas publicly for feedback. Helps with failing faster. Execution and luck are more important than the idea itself. In fact, I would say most ideas aren't really worth much (some are, but those are one in a million).
I think that's the difficulty a lot of people have with this: it seems to them like their idea might be one of those "one in a million".
Part of the difficultly for me has been realizing that the it's not just a rare, good idea that matters—but that it's a rare and good business idea specifically. For instance, I've had a couple projects that gained interest by researchers, which I took as evidence that they might be uncommonly good; but getting the attention of researchers is different from getting the attention of investors for a reason, and it's still questionable whether either has even above average value as a business idea...
The thing is, most people are actually good at generating ideas. It's really not the hard part. The fact that your great idea has probably already been done by someone before you is a testament to this fact. Sit me down for an hour and I could probably come up with 10 good business ideas, and I bet if I Google each idea, someone's already doing it. That's not a reason to be disheartened though. What you're looking for is an arbitrage opportunity in execution. Do you back yourself to execute better than the other guy that got there first? If yes, then press on. Nothing is more saturated than the market I chose (accounting/business management app). But the incumbents are cocky and out of date, and I felt my execution could win me a good share of customers. A definite gamble, but it's working out alright :)
