What is the rationale for all comparisons returning false for IEEE754 NaN values?

Question

Why do comparisons of NaN values behave differently from all other values? That is, all comparisons with the operators ==, <=, >=, <, > where one or both values is NaN

Answer 1

I'm guessing that NaN (Not A Number) means exactly that: This is not a number and thus comparing it does not really make sense.

It's a bit like arithmetic in SQL with null operands: They all result in null.

The comparisons for floating point numbers compare numeric values. Thus, they can't be used for non numeric values. NaN therefore cannot be compared in a numeric sense.