-George R. R. Martin, A Clash of Kings
It's a matter of mythology in The United States that presidents only serve two terms. Our founding father, George Washington, served two terms as president and then declined a third. Following his example, no presidents sought a third term until Franklin Delano Roosevelt in 1940. While FDR was one of the great presidents, he did violate an unspoken rule of American politics and the 22nd Amendment was passed soon after. And that's why our presidents are limited to two terms.
Section 1
No person shall be elected to the office of the President more than twice, and no person who has held the office of President, or acted as President, for more than two years of a term to which some other person was elected President shall be elected to the office of the President more than once. But this Article shall not apply to any person holding the office of President when this Article was proposed by the Congress, and shall not prevent any person who may be holding the office of President, or acting as President, during the term within which this Article becomes operative from holding the office of President or acting as President during the remainder of such term.
Section 2
This article shall be inoperative unless it shall have been ratified as an amendment to the Constitution by the legislatures of three-fourths of the several States within seven years from the date of its submission to the States by the Congress.
Like most mythology, there are some inaccuracies in this telling. Washington did care about the example he set as the chief executive, but he also had health issues. He'd die two years after leaving office.