Enthusiasm

Right now I am listening to one of those people who is so enthusiastic about life. Aren't those people amazing? How do they become like that? Do you think they are born that way, or do they develop that enthusiasm? Can anyone be like that? How can I do that? Maybe it's good that not everyone is like that because it's a little tiring - in fact, how do those people not drain themselves? It is also kind of exciting, though, to be someone like me, who is not like that because it's really amusing to observe such a person sometimes. I just think about it the whole time I listen to such people.