The snowball effect describes how debt payoff gets faster over time. When debt #1 is paid off, its minimum payment adds to the attack on debt #2. When debt #2 falls, both freed minimums attack debt #3. By the final debt, you're often throwing 3–4x your original extra payment at it.
This is why starting a payoff plan — even with a small extra payment — creates momentum that compounds. The last few debts typically fall much faster than the first ones.