An eyewitness description might be biased because of the witness' beliefs, values or experience. On the other hand, an encyclopedia tries to be as neutral as possible, to use different sources that describe the same event and to use only facts. For example, an Encyclopedia tells us Columbus arrived to America in 1492 and that one his way he saw many sea-cows (an animal), while Columbus' diaries describe how he arrived to India because he didn't know America even existed and that he saw many mermaids here (which in reality were the sea-cows).