If its a big idea, break it down into smaller pieces and try to prototype smaller parts - eg before organizing 100m, see if your idea works on 20 people. Also, try to boil the big idea down to an actual example where it does/does-not work or apply. Also - review the history/literature of your idea. This is key. You will always find historical analogues for just about any idea you can conceptualize. Someone will have had the same or similar idea before, and it will likely be in the historical record somewhere. Read the history, to go further, faster. And if the big idea is worthwhile, share it with others and get their views - but try to use your ears to listen. Don't listen with your mouth (as so many do). Recognize also that big ideas and results that come from them, often start - in science especially - from careful observations of small anomalies. Try to pay attention to see things that others miss - often these micro-observations are both the source of and can hold the solutions to something that turns out to be really significant. Also, if the big idea is also a problem, you might benefit from using the tricks and techniques of creative thinking algorithms of De Bono - invert the idea, transpose with random phrases, etc. And final comment - beware of "big ideas" that are just sophistry and obfuscation. You deal with those by using courtroom techniques to pull out the truth, and show that your counterparty is either just "talking his position", or perhaps outright lying.