The correct answer to this open question is the following.
The three branches of government are like the legs of this stool.
This statement means that the three branches must exist so the United States federal government can function correctly, as it was planned by the founding fathers and framers of the US Constitution.
The system of checks and balances was created with the division of powers in the federal government when the delegates were drafting the US Constitution during the Constitutional Convention from May to September 1787 in Philadelphia, Pennsylvania. This system allows the balance of power between the executive, legislative, and judicial branches, in order to allow none of them to have more power over the others.