Irrefutable is a four-letter word. Let’s leave it aside.
I don’t think that there’s any significant effect at all. I think that there’s a lot of confirmation bias in the observations supporting it. I also believe (close to know) that any facts meant to be evidence in support of it are anecdotal in nature, and not really from objective experimentation or observation.
But I think that there are instances of it – but attributable more to a self-fulfilling prophecy rather than an actual causal relationship.