In every Set For Life a draw a Life Ball is selected after the five main numbers have been drawn. You can win certain prizes if it matches the Life Ball on your ticket. Life Balls are numbered between 1 and 10 and are drawn from a separate pool to the main numbers, so you may see the same number appear twice in the same draw. You can also select the same number twice on your ticket: once as a main number and then again as the Life Ball.
The Life Ball is not interchangeable with any of your other numbers, so it only counts if you match the Life Ball on your ticket with the one in the draw.