Why did president truman not seek a second term of his own?

The amendment exactly excluded the sitting president, Harry S Truman. Truman started a campaign for a third term in 1952, but after 18 days he said, he would not pursue a second full period. He leave after a meagre performance in the New Hampshire primary. The only Presidents therefore far who have attended two full terms since the Amendment's approval are Dwight D. Eisenhower, Bill Clinton and Ronald Reagan.