What exactly does the masking technique do?

WN: What do you mean the first three were designed so that a person could have access to the English?
Scheidt: All four (sections) are done in the English language. The message could have been in another language. (But) this particular puzzle is in the English language…. The techniques of the first three parts, which some people have broken, (used) frequency counting and other techniques that are similar to that. You can get insight into the sculpture through that technique because the English language is still visible through the code. (But with) this other technique (in the fourth part), I disguise that. So … you need to solve the technique first and then go for the puzzle.
(WIRED Interview, 01/21/05)

I guess that answers which one we need to solve as well.

I’ve been wondering which is which, I think it’s safe to say that he ciphered and then masked.

So we need to solve masking and then the cipher.

This is why we fail.