In 2013 I published a list of ideas I wasn't going to do anything with. And did it again in 2014. I believe the expire date on an idea from 'light bulb moment' to action is about a year. If you haven't actioned something after 12 months, you should open-source it - put it out in the world for someone else to do something with.
But it's not true for just the ones sitting there collecting dust - people hoard ideas even as they work on them. Sharing exposes them to theft, they think. Or (worse,) criticism.
I have never experienced this to be the case - in fact every time I've shared an idea it's been made better.
A year ago I had a beer with a mate and told him about an idea, which included the clichéd napkin sketch. Like most ideas, it was fleeting and I didn't do anything with it. Until recently, when we had another beer and he walked me through how it had stuck with him, and he made some renders of his interpretation. Suddenly we now have a viable product and are hoping to bring it to market soon.
When you share ideas with people, they get better. Maybe they'll help you bring it to life. Or introduce you to someone who can. Or make a suggestion. Or just give you some good old fashioned feedback.
Hackerspaces are built on this premise. They're not just garages with tools, instead a community of knowledge which thrives through sharing.
More than anything though, sharing creates commitment. Having an idea is the easy part, the tough bit is making it tangible. While technology has made making ideas happen easier than ever, each time you share something you expose yourself just a little. And in doing so you give yourself another reason to bring it to life.
Don't be selfish with your ideas. They'll be better because of it, and you'll probably make more of them happen. I'll put my money where my mouth is too - if you're interested in the side project I'm working on above, get in touch and I'll share.