Identify what the narrator directly observes and what is an interpretation. A first-person account may be informative while still limited to one observer's position and knowledge.
Worked example
I could not hear the announcement reports the narrator's experience; it does not prove that nobody heard it.
Original fiction: At the Back of the Hall
I stood at the back of the hall behind a tall display. I saw the presenter point toward a screen, but the display blocked the lower half of it. The people near the front nodded. I could not hear the final sentence clearly. In my notes I wrote that the conclusion was unclear to me. I did not ask the front row what they heard.