The ability of the human mind to recollect events can be a powerful tool. It is also an inevitably faulty tool. This is why it’s critical for the investigator of high strangeness to acquire and document eyewitness testimony early on. The witness (and even the investigator) can become easily influenced by internal and external forces that alter the initial observation over time.
An example of this can be found in the varied descriptions of the infamous Mothman of Point Pleasant, WV from 1966-67.