What is something you just can’t get your head around?

For me it’s how planes stay in the sky with the amount of weight it’s holding. I understand because it’s the engines pushing it so fast (I think) so it stays up, even if one engine fails, it still can fly? How? Would the plane not turn and the other side of the plane fall down due to the engine not pushing the air from it?

Also how are large cargo ships stay afloat? How does it not sink? I might be dumb (I am) but it’s just fascinating to me, although I’ve watched countless videos on YouTube.