This is a lot of (LLM-generated) text, but there's a much simpler demo you can do for yourself: ask someone to type a "random" sequence of zeroes and ones, and then compare it to the output from /dev/urandom.

One immediately obvious pattern you'll see is that humans not familiar with this test will have a strong aversion to generating runs of zeroes and ones. For example, you probably won't see 0-0-0-0 or 1-1-1-1 in the human-generated sample, even though it has a pretty high chance of appearing in truly random data. It just doesn't "feel" random, right?

This has a practical application: if you're building a game with a component of randomness, people will often feel that the game is unfair or biased if they lose a number of times in a row. Tetris, famously, works around this by repeatedly taking a "bag" of seven possible tiles and shuffling it, rather than picking the next tile based on a dice roll. This way, the distribution over time is still random, but you never get more than two identical tetrominoes in a row.