Nerd Wrangling - Stone Soup
You might try to make stone soup and suggest it would be better with some carrots. But what do you do if nobody has carrots, or nobody wants to share them?
If you're trying to get people to contribute, you can't be too picky about what they bring to the pot. Someone might offer turnips when you wanted carrots. Take the turnips.
Some won't contribute at all. That's okay. The most you can do is say, "this might be better with…" and see who shows up.