* The shared peril: Trapped under the fallen tree with his lifelong enemy, Ulrich von Gradwitz, they are forced to confront their shared vulnerability. This shared peril dissolves some of their animosity.
* The realization of the futility of their feud: As they lie trapped, Gradwitz begins to realize that their centuries-old feud is pointless and meaningless in the face of their current situation. He acknowledges the absurdity of their rivalry and the damage it has caused.
* The potential for reconciliation: The possibility of escape and survival together creates a space for them to consider reconciliation. This possibility, coupled with the understanding that they are both victims of the same natural force, softens their hearts and allows them to see each other in a new light.
Ultimately, Gradwitz's change in behavior stems from a combination of his own changing perspective, the circumstances of their shared predicament, and the possibility of a new future free from the bitterness of their feud.