I was in a marimba quartet in college rehearsing Ravel’s String Quartet in F Major II, our concert was fast approaching, and I desperately needed to practice. But I had a problem: I couldn't find the time to get to the band room because it was a mile out of my way. I had only been playing mallet percussion for about a year so the practicing had to happen somehow. To solve this I made a practice marimba in an evening out of cardboard. I sketched out the dimensions/placement of the keys, brought home some mallets, and cleared my desk. I laid it out and rehearsed with a recording of the piece piped into my headphones. The result was in one evening I went from having a problem to inventing a quick and effective solution; using just cardboard and effort, I got a lot of practicing in and ended up having a wonderful concert.