An observation describes what you noticed, while an interpretation explains what you think it means. In everyday conversation the two often arrive together, making an uncertain explanation sound like a directly witnessed fact.
Try rewriting a first impression in two sentences. The first records the event as specifically as possible. The second begins with a phrase such as I took this to mean, making your inference visible to yourself and to others.
Consider at least one alternative explanation that fits the same observation. You do not have to treat every possibility as equally likely. The exercise simply creates room to ask a useful question before acting on an assumption.
When new information arrives, update the interpretation while retaining the original observation. This habit is useful in reading, discussion and collaborative work. It makes correction easier because changing your explanation no longer requires pretending that the event itself never happened.