Say you have an idea for which you can appreciate some intellectual and financial support. For this you may reach out to different sources, such as university professors or research institutes that also have experience in building start-ups.
For example, it can start with an email, in which the idea is not fully presented, but later you would be asked about it and may be completely open about what your idea is. However, how can we protect or make sure that the other person wont share that idea with someone else or steal it?
Certainly, in the beginning there is no patent that clarifies the ownership of that idea to be yours and patents are expensive as well to file individually. Or are there other ways to already associate the idea with your name and be sure it cannot be easily stolen?
----edit: The question also considers scenarios where signing an NDA is not really realistic. For example for students reaching out to professors or other institutes and having barely any idea how others may take advantage of their ideas.