Who was our 30th president? Calvin Coolidge, who assumed the presidency after the death of President Harding in 1923. Coolidge was a man of great sense. He was also the last president who actually reduced federal spending.

In this PowerLine post, Steven Hayward quotes Coolidge:

It is a great advantage to a President, and a major source of safety to the country, for him to know that he is not a great man. When a man begins to feel that he is the only one who can lead in this republic, he is guilty of treason to the spirit of our institutions.
It is difficult for men in high office to avoid the malady of self-delusion. They are always surrounded by worshipers. They are constantly, and for the most part sincerely, assured of their greatness. They live in an artificial atmosphere of adulation and exaltation which sooner or later impairs their judgment. They are in grave danger of becoming careless and arrogant.
A sound and wise statesmanship which recognizes and attempts to abide by its limitations will undoubtedly find itself displaced by that type of public official who promises much, talks much, legislates much, expends much, but accomplishes little.