What was the hardest videogame to play when you were growing up?

Looping. Absurdly rare arcade game where you fly a plane through a side-scrolling environment. The plane moves at a constant speed, and your controls are to pitch up or pitch down (plus a fire button to shoot bullets). Half the players who tried it would pitch down at the start of the game and go nose-first into the runway. If you even could get the hang of the control scheme, the game was all about flying loops in these tightly-designed areas where you’d have to know exactly when to turn and by how much. I made it to the final boss using MAME a few years ago, but it took like 20 tries.