It comes from the desperation of the mind when it’s in a very bad place. It grows bottom up.
Unlike long running state propaganda that runs top down.
At some point Ukrainian propaganda will start to cost them and they’ll need to hit the brakes. I hope they’ll be in a position where that’s a priority.
From the fact that nations that fight to the end and survive in myth live on to manifest again while those that give up the fight and surrender save lives but rarely become sovereign again.
Also in the idea of elite troops who it is hopeless to fight against. Myth is incredibly powerful in war and for the long term survival of a nation or state.
It's not propaganda in the same way as in Russia because the state did not make it. The notion comes from being in a war - it's absulutely terrible, disgusting experience, so people start making myths to feel some hope, and perpetuate them.
E.g. Russian soldiers are fighting for the myth that they are protecting some great country.