A filtration is information that only grows. Here a number ω between 0 and 1 is drawn at random and revealed one binary digit at a time. After n digits you know which of the 2ⁿ equal blocks ω lies in, and that partition is the σ-algebra ℱₙ. Pick an event, an interval (a, b], and watch how many outcomes it decides: blocks inside the interval answer yes, blocks outside answer no, and only the blocks at the two ends stay open. The conditional probability of the event given ℱₙ moves towards 0 or 1 as digits arrive. Knowledge only accumulates: every new digit refines the blocks and nothing is ever forgotten.