The so-called duck nature roughly means that a duckling that has just emerged from its shell will instinctively follow its mother when it first sees it. However, if the first thing it sees is not its mother, but other moving objects, such as a dog, a cat or a toy duck, it will automatically follow her. What is particularly important is that once the duckling forms a following response to an object, it will no longer be able to form a following response to other objects. The formation of this follow-up reaction is irreversible, which means that the duckling acknowledges the first but ignores the second. Later I thought about it, there are some people who feel like this when it comes to love, always regarding the first time as an irreversible will of God. In fact, that might just be a psychological suggestion.