How does an ultimate standard prove itself?

Dr. Lisle argues in his book that everyone must have an ultimate standard, and that standard by its very nature must prove itself. Then he states:

"This immediately invites a crucial objection: If an ultimate standard is used to prove itself, aren't we simply arguing in a circle? ...not all circles are fallacious. Remember that begging the question is not actually invalid, but it is normally considered a fallacy because it is arbitrary. But what if it were not arbitrary? What if the argument went "out of its plane," going beyond a mere simple circle, and used other additional information to support the conclusion? What if we found after making an assumption that we had good reasons for it? That would be perfectly legitimate." [emphasis in original]

My question has to do with the idea of finding reasons to believe an assumption after making the assumption. Doesn't this make those reasons (whatever they are) the ultimate standard? After all, we are using them to make our circle non-arbitrary (i.e. giving a reason that "our" circle is superior to other ultimate standard circles). The book seems to suggest that as long as we first assume the ultimate standard, and then afterward find reasons for it, then it remains our ultimate standard. But this seems to be only a chronological order, whereas the logical order of justification ends up placing the reasons for the ultimate standard as more foundational than the "ultimate standard" itself.

What do you think?