I know you won't believe me, but I truly enjoy compiling an index for my books. Most people I know hate it and will pay someone to do it or let the publisher do it. Once, in a tight moment, I asked my publisher to do the index and deduce the costs from my royalties. Of course I had to do it all over again myslef. I am the only one who knows what is important in my book and should go into the index. I am the only one who knows when “dream” is a cognitive process and therefore should go into the index, as opposed to when it is part of a content discussion and therefore shouldn't. I am the only one who knows that “the death of the author” should neither be indexed under death nor author.
Indexing is the first and only stage at which you realise what your book is really about because you see which terms and names pop up on every other page, rather than those in your subheadings. The first and only stage when you notice all small inconsistencies, such as alternating between “dystopian literature” and “dystopian fiction”. When you see that sometimes you provide authors for titles and sometimes you don't, and it will be a hell to index these titles. When you have to admit that some terms and concepts are superfluous because you only mention them once in passing and never explain. When you regret that you have mentioned names in the body of text rather than in in-text references because they quite unnecessarily get a separate index entry. Or the other way round, with the in-text reference only, an important source is not reflected in the index. And so on, infinitely.
Sadly, at this stage it is too late to make any changes. I used to compile the index with the first draft checking for exactly these small stupid details. For some reason, I didn't this time, and now I am punished for my laziness. Of course nobody will notice, because the only reason people use indices is to check whether they are in them and how often. (At least, this is the only reason I use indices in other people's books).
PS In Kurt Vonnegut's Cat's Cradle there is a character who can tell the author's personality from an index. I have no doubts.