Why does PostgreSQL not return null values when the condition is <> true

Question

I was confused behind the reasoning of the following:

SELECT * FROM table WHERE avalue is null

Returns x number of rows where \'avalue\' is

Answer 1

This link provides a useful insight. Effectively as @Damien_The_Unbeliever points out, it uses Three-valued logic and seems to be (according to the article) the subject of debate.

A couple of other good links can be found here and here.

I think it boils down to null not being a value, but a place holder for a value and a decision had to be made and this was it... so NULL is not equal to any value because it isn't a value and won't even not be equal to any value.... if that makes sense.