Why do people think that saying something out loud jinxes it?
Because the universe has a sense of irony. Duh.
It’s a superstition of course, but it can probably be explained by basic human pride. People usually say this about future events that they are trying to predict or hang their hopes on - events that are fundamentally uncertain. So if you say “My sports team is making it to the championships this year!” and then they don’t, you look foolish. To compensate, you say that when you said it out loud you “jinxed” it, i.e. claiming some control over an event which you obviously have no control over. As if they would have made it to the championships if you just hadn’t screwed up and made the fatal mistake of saying it out loud.
Or something like that.
Comes down to confirmation bias, I guess. All the previous times when you said something and the opposite didn’t happen you probably didn’t notice, but the one time it does, it sticks in your mind. I don’t tend to worry about such things too much in everyday life, but when it comes to sports, I’m bizarrely superstitious. Even I won’t tempt fate with 2 minutes to go and my team up 2-0 by saying the s-word* 
whispershutout*
Because people are stupid.
Because people are deeply programmed to look for patterns and connections in the world, whether or not they exist. That one time you mentioned grandma dying, and then a week later she did, it seemed like there had to be a connection, even if there wasn’t. It probably goes all the way back to some member of the tribe worrying that the hunt would be unsuccessful – and then it was unsuccessful!
It doesn’t jinx you as long as you remember to knock on wood, to drive out the evil spirits who are listening in, looking for ways to get you.
The Cowboys are going to win the Super Bowl this year.
Hah! Take that, Dallas fans!
What, you *want *to give yourself a kina hora?
I read a book about Murphy’s Law which had this related rule:
The Unmentionable Rule
As soon as you mention something:
If it’s bad, it happens.
If it’s good, it goes away.
I don’t know the answer but at least it’s not raining!
Not a baseball fan, I take it?
Is there a connection between baseball and the jinx thing? And yeah, I’m not, really.
Yeah, my sweetie, who has not a drop of Irish blood in him, gets seriously upset if I mention how well <whatever vehicle we’re currently pushing the limits of> is doing. He swears he’s not superstitious, but has no problem believing that I will jinx something just by mentioning it. :rolleyes:
It is absolutely, positively, 100% forbidden to mention that a pitcher is headed towards a no-hitter, and a thousand times over that, a perfect game in baseball. Jinx of the highest order.