Having something to say about the research, knowing what you were doing, why you did it, etc., being able to enthusiastically convey the spirit of your project is much more important than having a publication. Somebody could come on at the end of a project, do a little work, and if the PI is nice, he/she might list that person as a third, fourth author, etc. But it means nothing when interviews/essays come around and you have nothing to say about the project except "I ran PCRs day and night but I don't know why I ran them."