User blog comment:ReddUT/How to calculate probability of obtaining something you want from Top 50 decoders./@comment-31412431-20170717050725/@comment-27843946-20170717145413

Well it is a randomly generated number. However, the more iterations of generation you do, the closer to 1 the probability of it happening gets. Inversely, the closer to 0 the probability of it not happening gets.

It being what you want.