The phrase "I believed that" is often used to express confidence or conviction in a particular idea, statement, or opinion. It indicates that the speaker had faith or trust in the veracity of something at a certain point in time. It reflects a personal perspective and the subjective nature of beliefs.
The word "believed" is derived from the Old English word "gelēafa," which means "faith" or "trust." It has roots in Germanic languages and is related to the concept of trust or having confidence in someone or something. The prefix "be-" often indicates a thoroughness tied to the act of believing.