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

The over-simplified answer is that a NaN has no numeric value, so there is nothing in it to compare to anything else.

You might consider testing for and replacing your NaNs with +INF if you want them to act like +INF.