Here is another point to consider: If you were growing say Shiitake mushrooms on a container, a "bad" or potential unknown fungus might move in first to it and out-compete with your crop and thereby ruin your attempt.

But if your Shiitake mushrooms took hold and established a strong and healthy foothold the other mushrooms/spores/fungi will not be able to "move" in on after the fact.

So if you took this to a human perhaps the "good" fungus needs to be healthy and well colonized to prevent other random things from trying to grow in areas they shouldn't be in.