I had an idea stolen. It was pure philosophy... a means to help a woman understand how her man is motivated. Not a male / female thing, but that was a very marketable aspect, and (thus) the way I communicated the idea. It was butchered, but still sold $4m in books. The butchery got worse over two sequels. I seriously doubt that I will ever be able to communicate said idea (much less sell it) unless I can completely reconstruct its presentation.
Not saying that I disagree with the idea vs execution rhetoric here in the comments, I do agree... execution is more important. Execution in plant growing is more important than the seeds themselves... unless you lack the seeds.
Some here have said that at the right moment any arbitrary number of people will discover idea X. I would agree if the subtlety of the idea is not arbitrary, however the best ideas are unexpectedly early, and therefore subtle.
Do not mistake any of this as an argument for patents, or even fairness in a general sense. I know business is war. One's only recourse is carefulness, caution, the sacred texts called it wisdom.