I think it depends what doesn't work out. If you mean you don't like something in the song, of course it's important to say it (in a nice way of course). It's so important to make sure that both collaborators agree during the process of collaborating and a reasonable compromise is one of the way to achieve it. It's not possible to agree to everything. It's like in marriage - collaborating is a partnership and there will be agreements and disagreements. If you mean - the song is never making it - well, these days it's often the case with so many songs, it wouldn't be a fault of your collaborator. There are so many aspects in collaborating and one collaboration is different from another.
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Nadia
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Nadia