Of course, almost all people who are in this situation really don't have a great idea, but for the sake of this thread, let's assume that the idea is indeed great.
Why are we assuming that, again? Surely we should start by supposing we think we have a really great idea, and then making our first step figuring out to figure out whether we have an actual great idea or a bad one. And the best way to do that is to talk to someone who is an expert.
So while I don't have a solution to the general problem of what if you really do have a great idea, I do have the following advice: if you think you have a great idea, please be humble and skeptical about it. Please be willing to accept that it might actually be a dumb idea because of some detail that you, as a non-expert, know nothing about.
Personally I'm sick of reading disproofs of relativity and plans for perpetual motion machines.
If you're humble and skeptical about it, though, you'll never believe in it strongly enough to even get out of the house and talk to the experts. Better "strong opinions, weakly held."
I need to clarify the OP, since it seems many are responding to points I wasn't making.
Basically, like many of you, I have some ideas for things outside my field. I can see that, if pursued by someone in that field, they have an epsilon probability of success and a (1-epsilon) probability of failure, where epsilon can be very small.
What I was trying to say in the OP is that even if one of the ideas is within the epsilon range, that doesn't mean that if I pursue it, it will have probability of success epsilon.
Most likely, if I pursue it, it will have probability of success of delta and probability of failure (1-delta), where delta is much smaller than epsilon, and is zero in most cases.
That's why some ideas, if they are had by people in the field may be worth pursuing by them, since the odds of success, even if small, are not negligible. If those same ideas are had by people outside the field, the odds of success become negligible or zero, so they are never pursued.
As a small throw-away example, I live in an area where people put those silver or white covers on the dashboard of their cars, to prevent the sun from overheating the cabin of the car. I always thought that instead of this being a gadget you buy and then have to manually fold and unfold and store when not in use, cars should have those built-in, and you just press a button and some silver-coated cover emerges from the front of the dashboard and covers the front wind shield. Whether or not this particular idea would ever work, the point is that if someone inside, say, Honda or BMW or whatever, has this idea they can quickly make a CAD drawing and see how it would fit and work within the existing CAD drawing of one of the company's cars, they could probably price it, and if things look decent, they can pitch it to their boss. If someone from outside the car company has this idea, the number of obstacles they have to overcome just to get the idea heard is huge.
(Wasn't there a movie recently with Greg Kinnear where he played a guy who invented intermittent windshield wipers and had a very tough time with the car companies? I just found the person he was portraying: http://en.wikipedia.org/wiki/Robert_Kearns)
The question is how many innovations like the intermittent windshield wipers do we as a society miss out on because of the huge imbalance of how easy/hard it is for people inside/outside a field to pursue ideas?
Pop-up sunshields do exist for back windscreens, I remember seeing one on an S-Class Mercedes back in 1995ish. I find it hard to believe that nobody in the car industry has ever thought about putting one up front as well.
I think this is almost by definition the case, since if you are not working in some field, the way you get an idea for an improvement for that field is by being a user of a product of that field (e.g. by driving a car), and therefore you lack the knowledge base to make truly fundamental changes. You will most likely come up with modifications to existing products you use (e.g. the intermittent wipers)
But that's OK. It's not only huge advances (like the design of a nuclear power plant, which no outsider to that field will ever be able to accomplish) that matter; our life is also improved by many small advances. The more a society enables such things, the better.
Even ignoring that the idea may be very original and still be a very small modification to existing products, validating or implementing an idea takes a lot more effort than coming up with an idea whether or not it is a small modification to an existing product.
Do you think that if a dentist comes up with an idea for a more efficient internal combustion engine, or comes up with the idea for intermittent windshield wipers, that the effort to validate or implement those two ideas is the same?
Validating small improvements to existing products is usually much easier than validating fundamental changes to how things are done.
(Even ignoring the fact that, when the idea comes from someone outside the field, if the idea is a fundamental change to how things are done, it has a much higher probability of being a crackpot case, than if the idea is a small modification to an existing product)
Having an existing product gives you a framework to validate it, so makes things much easier. Yet, it is going to take more time and effort than thinking of the idea itself.
Someone outside of the field may still come up with an original idea (with much higher chance of it being a crackpot case), but would have no easy means to validate it, whether it relates to an existing product or not.
Because when you assume something, it allows for the conversation to progress to a more interesting point. What you're describing is obvious and common, so there's no need to harp on it.
+1 on the plans for perpetual motion machines, I actually get these once every few years from otherwise smart people who don't understand the basics of physics.
Why are we assuming that, again? Surely we should start by supposing we think we have a really great idea, and then making our first step figuring out to figure out whether we have an actual great idea or a bad one. And the best way to do that is to talk to someone who is an expert.
So while I don't have a solution to the general problem of what if you really do have a great idea, I do have the following advice: if you think you have a great idea, please be humble and skeptical about it. Please be willing to accept that it might actually be a dumb idea because of some detail that you, as a non-expert, know nothing about.
Personally I'm sick of reading disproofs of relativity and plans for perpetual motion machines.