Historians often find truths about historical moments that are against theirs what historians had hoped for; in such a situation, histories need to be committed to the information they have and must reveal whatever it is. Other times historians find details of history that are very violent and that may shock ordinary society, this is a difficult time for historians because they may want to disguise the truth they have uncovered.
The answer is "wanting to disguise the truth they have uncovered." Some historians find this tough. One of the reasons would be because not all people may or may not, like the truth. Some historians would omit some part of the truth to keep violent reactions from the readers or outsiders.
