does anybody really know what time it is?

This morning...

Scraggy Old Man in Street: Hey! Is today Saturday or Sunday or what?
Me: Thursday.
Old Man: Thursday. Thanks.

Three blocks later...

Handsome Young Latino on Corner: Is today Friday or Thursday?
Me: You're the second person to ask me that in five minutes! Thursday.

But then I thought...is it Thursday? What makes me so sure it's Thursday? No one else seems that sure about it.