The things work this way: when you click on 'draw' a dice is rolled and you have a certain chance to get 1 ninja. Let's take sage treasure. Very likely for every draw you do there's an 1.5% chance to get one ninja among sage naruto, ao and orochimaru. In addition to this there's an hidden counter to prevent the unlucky streak, so when you reach that counter you are guaranteed to get one rare. That counter for sage treasure is 60. So you can get earlier than your 60th draw a rare if you are lucky or if you are unlucky you will get it at 60.