Mein Kampf.

If you don't get close to others, you will never be betrayed and you will never hurt each other. But you will also never be able to forget your loneliness. Humans can never banish their loneliness for good, because being human means being alone. Humans are able to go on with their lives, because they are able to forget it every so often. Humans constantly feel pain in their hearts. The heart is so sensitive to pain, humans also feel that to live is to suffer. Well, I guess it just means love begins for no reason, but always ends for one.