The level of a unit's morale and motivation can give them needed leverage in combat situations. This leverage is also advantageous if their fighting force is not strong in numbers. Sergio Catignani comments that the system of values an army upholds can boost morale and improve motivation. As an example, the Israeli Defence Force aims to uphold the values of "responsibility," "credibility," "professionalism" and "sense of mission." They place emphasis on strengthening the cohesion and spirit of their units through the oath a soldier takes at the beginning of their military service. Oaths for some brigades are taken at historically significant locations such as the Western Wall in Jerusalem where the 1948 Arab–Israeli War occurred, to reinforce accomplishments of past comrades. Leonard Wainstein says morale may be threatened by sudden or traumatic losses. These losses may involve individuals of a military force turned into casualties by their own weapons such as artillery and mines. The death of a commander could have a large effect on their unit as they are relied upon to lead. Morale can also be undermined by individual level factors such as fatigue resulting from a lack of sleep, fear, and stress.