What Should Every Programmer Know?

what is the basic core of knowledge that every programmer needs to possess to be called a developer.
opinions vary ,but i don't thnk knowing a particular programming language is it.
I know there a bit of maths involved but how much.
what else ?
what should the man standing before me applying for a job possess to get the good mark?

First ,  i think u need to posses an Engineering skill.
because programming deals with Engineering and what Engineering entails.
I hope that helps.