There is something about Frank recognising Nietzsche in Mel's words and Robby having "Amor Fati" as his tattoo, which is repeatedly mentioned and explored by Nietzsche as a philosophical concept and approach to life in "Ecce Homo: Wie man wird, was man ist" and "Die fröhliche Wissenschaft" and "Also sprach Zarathustra: Ein Buch für Alle und Keinen".
Thinking that maybe Michael got his tattoos done relatively recently (the linework looks crisp in the show, which I will use for the benefit of my headcanon with no shame, sue me), and maybe that's what moved Frank to get into Nietzsche's philosophy out of curiosity.
I keep wondering what their dynamic looked like before S1, and evidence of their early interactions in S1 leads me to believe that there was (and still is, but that's a different conversation) a strong mentorly bond. Maybe Langdon also did his rotations at PTMC, giving more time to acclimatise to each other for a bond to form, whatever. So it's not a completely wild idea that Langdon would have noticed the fresh tats during scrubs change or just plain movement. Maybe it was the first time they both talked about something outside of medicine and work.
Just makes me happy (and also sad) to think that maybe that small part of that still wet-behind-the-ears Langdon is in there somewhere. The one who read up on Nietzsche after seeing his new mentor's tattoos. The one who found the tattoo and the idea behind it cool (he is a history nerd; obviously he would find something like that cool). And maybe it's ironic for him to hear "What doesn't kill me makes me stronger" and then Kelly Clarkson's name. Maybe in that moment he wishes he had never read up on Nietzsche.












