Pólya urn model

Pólya Urn Model is a mathematical model which shows the reinforcing nature of success and network effects.
Imagine an urn or a bag with marbles of different colors each. A marble is picked randomly, and it's placed back along with another model of same color. The process repeats multiple times, and as you can imagine the probability of picking a color picked first increases over time in most of the cases.  Success begets success.
The program below simulates the model.

Pólya's Urn - Because this post needs a thumbnail