I know what I saw!
That is even the title of an UFOtv studios video. That title implicitly implies that a given witness can determine and identify exactly what he/she saw, it is giving to the witnesses capabilities that are unreal and that practice shows in a daily basis that are wrong.
People that regularly make observations know that the process of "identification" of apparently anomalous occurences is very hard, many times only a carefully frame by frame examination of a footage will reveal details that are simply impossible to see in real time movement.
Perception, what a given person perceives is deeply connected to that person knowledge, preconceptions and expectations, we had seen that many times.
So if even in cases where detailed footage of a given event done by an experienced observer is hard to "decode", can we really trust personal accounts even from ourselves that happened just yesterday? Even more in a more distant past?