If you're a budding writer, the chances are that at some point you have heard the axiom "write what you know". So it's no surprise that at some point Sir Arthur Conan Doyle presumably heard it too and sat down to write his first novel at the age of 23, saturating it with his opinions in the process. That novel was subsequently lost on the way to the publisher (it remains missing to this day), so he sat down and tried to reconstruct it from memory.
It remains incomplete because the editors have just transcribed it to the page, rather than tried to fill in any gaps themselves (much like Douglas Adams' The Salmon Of Doubt, in fact), and there are missing sections in addition to crossed-out paragraphs (and in fact, the narrative ends with a note that states that it ends there in mid-page).
This novel has been described as semi-autobiographical, but "93% autobiographical" would have been a better way to put it. The merest appearance of a narrative and the token attempt to create an original character is probably the only thing stopping this book being completely autobiographical. At times, I forgot that the main character, the eponymous John Smith, was supposed to be 50 years of age and afflicted with gout.
It is perhaps a mark of either my respect for Doyle or just his natural skill as a writer that I didn't find this barefaced expulsion of opinions annoying or grating in the slightest. For instance, when people normally start discourses on why God exists, I normally sigh and say "oh, here we go" (I am well aware that people do the same thing with my atheist writings) but much to my surprise when Doyle did it I found it engaging and a very good analysis of how early religion might have come about. I suspect that it's the closest I've ever come to being converted.
It's interesting to analyse this in the context of what came after this, as even here you can see Conan Doyle's style developing into what we expect to read when we pick up a Sherlock Holmes novel. There's a good doctor to receive the protagonist's insights of genius and opinions of the world and the novel is written in the style of a journal.