I could be wrong but if the president vetos a bill then Congress can be like well we need this to happen so if there is a 2/3's vote then they can overturn the president's veto.
A two/thirds vote of each house of Congress is required to pass a bill over the President's veto. If the President vetoes a bill, a 2/3 vote in the Senate and House of Rep. is required to pass it over his veto.
