I didn't know that I could bind things to hotkeys until my second playthrough. I didn't realize that I could bind things other than weapons until my third. I didn't realize that holding Tab turned on my Pip-Boy's flashlight until my fourth. What about you guys?

I didnt know about the ability to ship items until my like 7th playthrough

Hotkeys?

I didn't know shooting mines would do anything until my third playthrough (Justified, since shooting an explosive usually just gets you an explosive with a bullet hole in it IRL). I didn't know how damage threshold differs from damage resistance until my sixth playthrough. I didn't know what Turbo did until the Lanius fight in my first playthrough. I didn't know how to use skill magazines until the beginning of my eighth playthrough.

It's honestly a miracle I've had any success with this game since I can be so aggressively stupid

Took me forever to figure out that I could apply doctors bags directly to limbs(learned that in F3), always thought they did so little lol

Took me three or four times in dead money before I realized why Dean Domino would always try to kill me, even if I wasn't rude to him....