Almost a 100 years ago , someone discovered DDT. DDT was effective in killing mosquitos , but could not wipe out the entire population. This is because a certain percentage of mosquitos, let us say 4% for now , was resistant to DDT. This 4% became 100% of the entire mosquito population 3-4 years later after DDT was introduced. All of a sudden, DDT was not so effective anymore.
This same technique...