This is just a superstitious believe by some gamblers because it's not totally true that when you have a negative feelings it will affect your luck, these luck in question happens randomly irrespective of how someone is feeling but being anxious is just like a natural feeling that some people have when they go gambling because they are scared off losing.
You can't even imagine how many superstitious people there are in the world. I personally saw how casino players resort to various rituals. I even feel a bit awkward for them. I feel some kind of Spanish shame. Well, what you won't see in the gambling business. But no rituals work at all. People continue to lose money the same way they did before. Therefore, you should think with your head several times, and only then start playing.