Three main reasons that there are changes to a budget (and hence, changes to the overall budget) are: (1) errors the cost estimator made about how to achieve the tasks identified in the project plan; (2) an increased knowledge about the project's goal and deliverables causes changes to the way of thinking, leading to wholesale changes in the project; and (3) a new law, standard, or mandate occurs leading to a change in the way the project is carried out.

Can you think of any other reasons why the baseline of the budget might need to be changed midstream of a project? (add ref with answers)