Well, there could be various reasons. Maybe the man was mentally unstable or under the influence of something. Or it could be part of a fictional plot with a complex backstory we don't know yet.
It could be due to a heated argument or a deep-seated grudge. Maybe the man was driven by jealousy or anger.
It could be that the pride led the man to take risky actions or ignore warnings, resulting in the fall. Or perhaps there was a villain in the cartoon who used the man's pride against him.
Maybe they had a fight or some kind of conflict that led to the pushing.
Maybe the girl was under the influence of some magic or mind control in the cartoon world. Or it could be a dream sequence where anything can happen without rational explanation.
It could be that he's being chased and sees no other way out. Or perhaps he's under a spell or curse that makes him do it without thinking clearly.
Well, there could be various reasons. Maybe the old man was a villain and this was his punishment. Or it could be a symbolic act to represent a major change in the story. It all depends on the context and the creator's imagination.
Maybe he's trying to be adventurous or show off and didn't think about the danger.
I have no idea. Maybe it's for some sort of shock value or to create a dramatic scene.
Maybe he was being adventurous or dared by someone.
Maybe the deer was defending its territory or felt threatened by the man.
It could be that the man did something to disturb the stag's territory or routine, provoking the chase. Or perhaps it's just a part of the comic's fictional plot with no specific reason.