Morelli explains this principle or commandment as follows: "With rare exceptions, people tend to join the victorious cause. In the case of war, the preference of public opinion depends very much on the apparent results of the conflict. If the results are not good, the propaganda must disguise our losses and exaggerate those of the enemy." [0]
It's the same in Russia, if you are wondering
[0] https://en.wikipedia.org/wiki/The_Basic_Principles_of_War_Pr...
[Edit]: I guess I meant to say, I'd love to understand Russians' point of view. I don't understand at all.
And with all respect, I'd hazard an unsubstantiated guess: you don't really know what average Russian thinks either, as you're probably in contact with Russian intelligentsia.