Not looking at things
When I was 12, I used to be really superstitious on Wednesday mornings (for this was the day I woke up at my mum's flat, which for some reason made it different). I thought for some reason that if my routine didn't go as I am about to describe, the day wouldn't go as well as I wanted it to:

1. The night before, I wouldn't look at the clock after 10:10
2. I wouldn't look at the clock or my watch for the whole morning
3. I wouldn't watch the TV (which my sister would watch) or even get in a position I could see the screen
4. I wouldn't look in the mirror when I brushed my teeth or washed my face
5. I wouldn't look down when I was urinating. But if I missed the bowl, even just a little bit, instant bad day.

On days when I accidentally did one of these things, I would get really annoyed. On days when I was successful, nothing actually happened. I didn't actually question all this until the summer holidays, when I concluded that there was no point to this at all. So I only did it one more time, just to check.
(MOTOR Master Of The Open Road, Sun 18 Dec 2011, 14:55, 1 reply)

This is self fulfilling
If not achieveing all those things makes you angry, of course you'll have a bad day.

But if you didn't try to do them in the first place (and let's face it, they all a bit pointless), you wouldn't get angry.

That's probably obvious.
(username failed moderation, Mon 19 Dec 2011, 9:12, closed)