I didn’t understand the concept of a climax until it happened. The first time crankin it I remember mid way through thinking “I don’t get it, so if I keep doing this it just keeps feeling better and better infinitely?” When it happened it was one of the most stunning moments of my life.
Until my first ejaculation, I thought the only time something came out of my penis was when I was peeing. I was so surprised when something else came out and holy shit there was so much of it everywhere. I didn't know that could happen and it made a mess all over my surroundings.
Last minute addition: I thought a woman could get pregnant if a man licked between her boobs. This was before my first ejaculation.
I had my first real ejaculation while I was sleeping as a kid. The one time I slept over at my grandma's. She never said anything but boy did I have impecable timing.