Why do people and nations often act against their own interests?

Question

Late noted historian Barbara Tuchman, in "The March of Folly, From Troy to Vietnam", documents that governments have a long record of acting self-destructively and foolishly, despite warnings by other people in their own times, and sometimes even the promptings of their own common sense. The Renaissance popes, for example, neglected the Church so badly that they inspired the Protestant Reformation, the Trojans (according to legend at least) accepted the gift of a big wooden horse full of enemy troops, and Montezuma, despite warnings of advisers, let a small force of Spaniards overwhelm the vast and aggressive Aztec empire. She said that folly existed when they knew (or should have known) better based on information and warnings available at that time. She also thought the British were foolish to risk the loss of the American colonies. (If hindsight could be converted into foresight, I could retire on lottery winnings!)

Answer 1

1 Leaders make decision that are in their own interest, which is not always the same as the country's/institution's interest.
2. Decisions have unintended consequences. People and their leaders do not see the real effects of their actions but see only their intended objectives until it is too late.
3People are often moved to action by emotions, not rationality.

Answer 2

they have no other options.