I've been trying to delve deeper into predictive processing theories of the brain, and I keep coming across Karl Friston's work on "free energy".

At first I felt bad for not understanding this. Then I realized I wasn't alone. There's an entire not-understanding-Karl-Friston internet fandom, complete with its own parody Twitter account and Markov blanket memes.

From the journal Neuropsychoanalysis (which based on its name I predict is a center of expertise in not understanding things):

At Columbia's psychiatry department, I recently led a journal club for 15 PET and fMRI researhers, PhDs and MDs all, with well over $10 million in NIH grants between us, and we tried to understand Friston's 2010 Nature Reviews Neuroscience paper – for an hour and a half. There was a lot of mathematical knowledge in the room: three statisticians, two physicists, a physical chemist, a nuclear physicist, and a large group of neuroimagers – but apparently we didn't have what it took. I met with a Princeton physicist, a Stanford neurophysiologist, a Cold Springs Harbor neurobiologist to discuss the paper. Again blanks, one and all.