What is the most complex topic you understand?

Probably options/derivatives trading.

Feels weird to say this but given the fact that I continue to see investment strategies pitches saying "covered calls provide additional income and benefit from market volatility" from people with 10+ YOE the bar for "understanding" is very low.

Hmm, I'm wondering how "complex" is defined here. Some abstract topics seem complex until you drill down and see how they are defined (in which case they become trival), and some topics or experiences seem obvious until we drill down and try to figure out where they come from or how they work and realise they are intractible.

I could not only see "probability theory" and "the hard problem of consciousness" falling on either side of the divide, but I could imagine vast flame wars (punctuated by occasional scholarly papers) arguing for and against either "this is seemingly complex but actually simple", or the other way around, or neither, or both simultaneously.

I could say something fancy about how I used to be scared of category theory but now I just think it's spicy graph theory, but I don't feel like inciting such flamewars with randos on the internet this Christmas season ;)

Probably cryptocurrency