Some thing I made sure to not mention publicly: The exact domain name I planned to buy for several months before getting around to it. Anyone could have bought it and squatted on it if I had mentioned it publicly. Only a few people close to me knew what it was while I developed a new site without having a domain name. I did spend some time wondering if that was really the right name while I worked on developing the site idea and eventually decided it was.
As I have stated here previously, one of my plans is to learn a programming language and write a simulation for my health site. I don't think it can be stolen because it will be rooted in the things I do for my own health -- ie it is rooted in first-hand personal life experience. Even if someone stole the general idea to create a "game" to help people with wellness, I don't think they could really steal my idea to create a game to help people with my diagnosis get healthier. I know plenty of people doing alternative stuff and seeing better than average results. I don't know anyone who has had the kind of results I and my son have had. So I don't think anyone else knows what I know, therefore any other simulation would not contain the mental models I have in my head. Thus, I don't worry about that.
On the other hand, I mostly talk about that plan here and have also mentioned it in passing on a health list for a different type of medical condition. I don't think I have mentioned it on any of the CF lists I belong to. I think it would get point-and-laugh type reactions: "Yeah, sure, you are going to cure my deadly medical condition by having me play a video game. Har-dee-har-har." I also have no idea how long it will take me to implement. I have yet to even learn any code. So that is another reason I am keeping that plan to myself in the communities where a few people might be interested in it. I don't want people to be tired of hearing "empty promises" by the time I actually implement it.