ものと思っていた

This expression is used when talking about a belief or assumption you held in the past about a situation or outcome, which did not turn out as you expected. It emphasizes that your prior conviction or expectation has changed since then. It often appears in storytelling or reflections about past events, where the speaker contrasts past assumptions with what actually happened. Note that the speaker’s current stance may be different, and the nuance can carry a sense of surprise or realization.