The things I have enjoyed studying are mostly those that have required me to contend with myself for a long time before making what I felt to be progress. Here is a paragraph from Primo Levi that tells me he has the same experience.
He attends a school reunion, reflecting on the fact that many of his classmates are no longer chemists and no longer have chemical tales to recount. But the organizer of the reunion still has some tales, and Levi invites the organizer to contribute a story to his book:
I asked him if he would like to contribute to this book. If he would, he should tell me a story and, if he would allow me to make a suggestion, it should be our kind of story, in which you thrash about in the dark for a week or a month, it seems that it will be dark forever, and you feel like throwing it all up and changing your trade; then in the dark you espy a glimmer, proceed groping in that direction, and the light grows, and finally order follows chaos.
(Primo Levi, The Periodic Table, tr. Raymond Rosenthal; “Silver”.)