So, a simple 3x3 Rubik's Cube is SOooo 1980-something. The stealthy geeks in the 90s just couldn't stop with a 3x3. After all, if you can solve a puzzle in less than a minute you're not really getting a mental workout anymore. The 4x4 is the essential step up when you're looking to bring your workout to the next level. A tad bit of additional dexterity is required. And a LOT more time on your hands.