This is rather like the chance of throwing a 6 on a die. If you threw 6000 dice, however, you would predict that near enough 1000 would land on a 6. The random event becomes predictable when huge numbers are involved. This is 602 thousand million million million , a number referred to as Avogadro's number, after the scientist who calculated it. The random chance of one 14 C atom decaying therefore becomes predictable.
Statistical decay follows a familiar pattern.
Suppose you shook the 6000 dice. Then suppose you removed all the dice that landed on a 6 and counted how many were left. The remaining dice are then shaken and thrown again. Once again, the dice showing 6 are discarded and the remainder counted. A graph of number of dice left vs. number of throws is plotted.