The Nefesh Hachaim and a Musar book of collected ideas from the Gra called Even Shelma אבן שלמה "Perfect Rock" or Perfect Measure".. The first one is rather important . The Nefesh Hachaim is very important in so far that he explains a lot of issuesף- for example-the importance of learning Torah, how to pray properly and a lot of other stuff.
The trouble I found with the Nefesh HaChaim was it made me feel guilty when I am not learning Torah. And that is confusing to me because my parents and the Rambam were more along the lines of Torah with a vocation plus Physics and Metaphysics. Still I admit the Nefesh HaChaim might in fact be the most important of all Musar books.
There was a later Musar book that was saying to give your children the Nefesh Hachaim and on their bar Mitzvah [or Bat Mitzvah] to have them read the 4th part which talks about learning Torah. I had hoped to do that- but the truth be told- I got distracted from learning Torah. I am not proud of that. If I could go back today I would try to stick with the path of my parents as close as possible תורה עם דרך ארץ Torah with a vocation. That is to learn Torah half a day and to learn an honest vocation for making a living. That is I would learn Torah but do my best not to be in a position of using Torah for the sake of a livelihood..
So what makes it so hard for me or others to learn Torah. The problem is clearly half and half. That is half the problem is in me. When I or anyone walks away from Torah it is no surprise that when we try to come back into the world of Torah that we find the door is locked.
The other half of the problem is the Dark Side the Sitra Achra now has taken over a large part of what used to be called the world of Torah. Nowadays the leaders are the villains. That means to learn Torah you have to get a Gemara and a book of Musar and the sidur HaGra and do your thing at home. There are very few authentic Litvak yeshivas around anymore. There obviously are in New York like the Mir and Torah VeDaat and Ponovicth in Israel. But besides the great Litvak yeshivas it is hard to find anything authentic.