Educational explanation
Compound interest helps money grow because interest is earned on the principal and on any previously earned interest. Over time, this can create exponential growth in the later years of a plan. The earlier you begin and the more consistent your process, the more time compounding has to work.
Example
Imagine you invest $200 per month for 20 years at a modest annual rate. The money grows from periodic contributions plus compounding, so the later years often add more value than the early years because the invested amount keeps increasing.