If something is built on sand, it does not have a strong or proper basis, and so is likely to fail or come to an end. The twin budget and trade deficits are evidence of an economy built on sand. His whole empire was built on sand. It folded, and in 1981 he was charged with war crimes. Note: This expression relates to a story in the Bible, where Jesus compares the people who follow his teachings to a wise man, who built his house on rock, and those who did not to a foolish man, who built his house on sand. When floods came, the house built on rock remained standing but the house built on sand collapsed. (Matthew 7:24-27).