Because the brain is a pattern machine. Asked for randomness, people avoid repeats, over-alternate, and cycle through sets — all measurable departures from true randomness.

Three indicators are reported. The RNG Index (Evans, 1978) measures how unevenly you used the nine digits: near 0 means all digits appeared about equally often, and higher values mean more bias. The Counting Score is the proportion of consecutive responses that continue a simple arithmetic step (up or down by 1 or 2); lower is closer to random. The Turning Point Index compares how often your sequence changes direction with what chance would produce: values near 1 match chance. These are educational indicators, not a diagnosis.

The task loads heavily on executive resources; random generation degrades under dual-task load and fatigue, and has been studied in clinical research populations.

Feedback helps a little, but the biases are robust. The task is more valuable as a probe of cognitive control than as a trainable skill.