As we know,we have 1/30000 chance to come across a shiny pokemon everytime we come across a pokemon,but that makes more and more people must come across more than 50000 pokemon to catch their favorite shiny pokemon,so they stay in game to try to catch it,it occupies the resources of the server.so if we can ensure that everyone can get a shiny one if he comes across more than 30000 pokemons?we can slowly improve the rate of it every time we come across one ,meanwhile if return to the original rate when he meet his shiny one.
