Depends a bit on the situation. Let me give an example, I don't need feedback that the idea is ridiculous.
You: I got such a great idea for making tons of money and changing the future.
Rich friend: What is your idea?
You: Cars running on jellyfish! It is the best energy source in the world. I started my research 6 months ago and it seems perfect. Already calculated it through and this will reduce the fuel prices with 50%.
Rich friend: wow, that sounds great! When are you going to build the car?
You: Well I got a great place to build it, I even already got some engineers, but the sad thing is I will only be able to start it when the bank will give me a loan. They are positive, but they want to research it by themselves first. Might take a few months..
Two months later:
You: I finally got the money to build the car!
Rich friend: Oh right, yeah, I forgot to mention. I already build one, BMW signed me a 1 trillion dollar contract!
'
You: 
I think it depends on the risks the person building the idea has taken compared to yours. In this example, I think it is wrong, and you should get at least 50% of the profit.