President-elect\'s job creation plan changed from 2.5 million to

Today, one article said it maybe create up to 4 million news jobs,  most of them in private sector. How could be the number kept changing in the past 6 months with economic situation worsening. I don't know whether what he proposed is trusted because in short time, the plan kept changing, and the number was jumping. All the politicians are good at creating exciting number to get support.