Okay. As we know, no one individual Pick 3 number has any more ,or less, of a chance of coming out than any other one. It doesn't matter if that number is a non-repeating number, a double, or a triple. The odds are still the same at 1000:1 with a straight play. Of course, once you move away from individual numbers and play more numbers ,each time, your odds change. In effect, this means playing a group of numbers.
So, we know that you must play multiple numbers each time. If we decided to play two numbers ,each time, we would double our chances of winning from 1000:1 to 500:1. Similarly, by playing three numbers we triple our chances to about 333:1. The more numbers we play the better our odds.
First off, to beat the game you have to approach it on a group level. The largest group is the entire set of 1000 combos. But, we know that we can't expect to play all numbers and make money. Therefore, you have no choice, but to break the numbers down in some sensible way. Secondly, you want to look for patterns involving your groups of numbers. An example of this approach is the 120 core.
The bottom-line is that you only want to break the numbers down just enough to make groups that are playable. This means that they're not so large that they throw off your potential profit. The approach here takes into account the ideology of playing as many numbers as you can. If you want to play and make money often than this is the way to go.
Of course, this is not the whole story. There's special coding involved that's an essential component to make this work. But, this is some of the logic involved.