Please look up the law of averages. In your example you say if there was 10 exotics you should expect it one in ten times but that's not true at all. They would all have a ten percent chance each time an exotic dropped, so odds never increase.Think of it's like flipping a quarter you have a 50 percent chance but out of ten times you could get 7 heads, it doesn't mean it still didn't have a 50% chance.