I once memorized 250 digits of pi to prove to myself that I could. I used memory palaces, which were really just houses of people I knew with weird images representing numbers placed in all the rooms. I would walk through the houses in my mind, coming across all the bizarre images I'd placed there, then relate the image to a number that I'd connected to it.

When I finally had the whole thing down and had memorized all the images that represented all the numbers, I memorized and recited 250 digits of pi to my friend who followed along checking me on a piece of paper I'd printed for him. He said it was one of the most boring things he'd ever had to do, but that I hadn't made a mistake. The next day, I started forgetting everything, and now I only remember that in my childhood bedroom Clint Eastwood is fucking an alien, but I don't know what number that image is supposed to represent.