Why isnt this "X" symmetrical?

[BrenFunk]

Hey, wondering if anyone can explain why some X's are designed asymmetrically? Noticed it in a few fonts, the example shown here is a capital X from Frutiger Ultra Black. Thanks.

[Ralf Herrmann]

It’s one of the many optical corrections type designers usually add. Not everything that would be mathematically correct, looks correct. In this case, you have interacting diagonals which is troublesome. Google “optical illusion parallel lines” for example. 

Here is Arial without compensation (left) and the actual version (right).
Which one would you prefer?

[BrenFunk]

Thanks Ralf, makes sense.