Wittgenstein kept these notebooks, three of them, during his military service in WWI. They are intriguing and quite moving. The entries here are what he wrote to himself in private code on the verso (left) side of the notebook. They have not been published before. (The entries on the recto (right) side of the notebooks were his thoughts leading to the Tractatus-Logico-Philosophicus; these entries were published long ago.)
Two major elements of his personality and thought emerge via these brief, pungent comments
Personality: At age 25-27, Wittgenstein volunteered as a kind of test. He seems to have wanted to know how he could mesh with other soldier/sailors and what his reaction would be to the perils of war. Although he was born to a wealthy family and inherited great wealth as a consequence, he was a humble person and a courteous person. This didn't help him get along with his shipmates on a river patrol boat. They were bores and oafs and apparently picked on him and annoyed him incessantly. So he withdrew to the best of his ability and circumstance. The problem was that he did have homosexual urges that made him quite lonely, and in wartime he could hear little from loved ones via letter. So he monitored his masturbation in these notebooks and he alluded to shore leaves that involved visits to "baths." Neither activity seems to have given him a lot of relief. But this aspect of the notebooks shouldn't be overstated because Wittgenstein had an ascetic streak that was driving him to discover how he could shed his sense of self altogether. This led to hazardous duty and consideration of suicide. He seems to have been sincere in wanting to bait death and either prove his courage or succumb to his cowardice. This desire complemented his evident religiosity. He wanted to leave himself in God's care and wrestled with the idea of God all the time.
Looking at these notebooks on a philosophical plane, we can see important outcomes. Through war and deep thought, Wittgenstein was cultivating detachment and accepting the limits of what we can know...or affect. It's easy to see the influence of Schopenhauer (and thereby Hinduism) on him. He developed a notion of existence as illusion and fate as a force beyond the ken of mankind. In particular he seized on the idea that the fundamental illusion is what we tell ourselves with words.
The challenge of Wittgenstein has been that he entered into the realm of pure thought via logic but he never shed his deep feeling that a spiritual or quasi-mystical understanding offered better, if frustrating, results. He was a man in self-conflict, as these notebooks reveal (and as his entire biography reveals). The fact that Wittgenstein often presented philosophical findings enigmatically, through results that were not bolstered by an accompanying explanation of the methods that led him to these results, may perhaps be attributed a kind of self-cancellation. The ideas that he explored were hard won and powerful but if the truth about existence is that it is an illusion woven of words and his ideas were ultimately conveyed by words, what were they worth?
Later in life, after the war, during his long tenure at Cambridge, Wittgenstein devoted intense energy to philosophizing for the benefit of his students on the spot, as it were. Perhaps the quirkiness of his long silences broken now and then by philosophical eruptions can be traced back to his military service. I say "perhaps." I don't know. But for Wittgenstein the value of "now" in wartime was immense. Anything can happen now in wartime and little that happens before or after now signifies much. Let's say the past and the future are inexistent when you are under fire and add the thought that the past and the future are illusions of almost no value. Let's go beyond that and place the wartime truth that you are not in control of your fate in the context of Wittgenstein's larger conclusion that you are not in control of your fate at any point. Schopenhauer would have said the same. Nietzsche tried to go beyond Schopenhauer, but Wittgenstein was drawing the conclusion in these notebooks that nothing self-based matters. Nothing. One could not even wrap oneself in the Divine with the confidence that this would lead to good. It might lead to evil. Ethics, he writes here, is a nonstarter. How does he explain that? He doesn't, but I am trying to do so here based on the fragments recorded in three little books that were overlooked, never published, until 100 years after they were jotted down by a lonely man on a boat, in a barracks, occupied for most of his day by tasks that should have been humiliating for him but weren't either because he wanted to be humiliated or he thought no one can be humiliated since humiliation is just another illusion.