Friday 13th

So today is Friday 13th, a supposedly unlucky day. Here's the truth about it.

The day as such, isn't unlucky that would be ridiculous, it's still just any other day.
Though the IDEA of the day being unlucky, does make it so. A bit of psychology/sociology here.
When people expect something, their actions from this assumption will generally lead to it happening.

This is why today is unlucky, but no different to me believing the 18th August is unlucky (I don't).