Vampires can feel lonely because they don't have other people to be with. That's when they will feed and turn people into monsters like themselves; also, when a vampire turns someone else into a vampire, it's as if a depressing person simply talks negativity to a positive person and that positive person becomes negative. This is why vampires are immortal because they never die, but they have weaknesses like getting stabbed with a stake through the heart. When it comes to a depressed person, that same stake that puts the vampire to rest can be represented as love towards the depressed person who gets stabbed with it and leaves the dead, negative part of themselves ; then they become alive and move away from negativity, leaving their dead minds behind. Humans have certain addictions in their lives, like vampires.