For me, a hurdle to get over was trying to understand in the context of my experience of the world. Like, popsci has this whole "is X a wave or a particle? Scientists still don't know..." schtick. And our understanding at some level is, "here's the math to describe this system."

Getting away from always mapping that onto the world we experience is, IMHO, really important. Not that it should be understood solely as math, by any means! But you really need to throw away intuition gained from the macroscopic world we interact with.

My favorite example was looking at reflection coefficients and seeing that an "infinite wall" is the same as an "infinite cliff"

you'll reflect off of both. Which makes zero sense if you imagine driving a bumper car into a wall (bounce back) vs. over an infinite cliff! But it does me make sense in its own way, and after building up intuition, so do other "weird" and counterintuitive things.