Success is not the key to happiness. Happiness is the key to success.

Every mathematical problem is a window into a new world of understanding.

"The past is a foreign country; they do things differently there."

The highest form of theory is the ability to simplify complex things into simple and clear principles.

The state, therefore, has not existed from all eternity. There have been societies that did without it, that had no notion of the state or state power. At a certain stage of economic development, which was necessarily bound up with the split of society into classes, the state became a necessity.