Secret for happiness

Of course everyone wants to be happy, I believe.
As I observed one person, I found one secret to become happy.
Let's say his name is Tony. Here's what Tony does:
* when he talks to store clerk, cashier, tollway attendants, etc. he always add their name in his conversation. The other day when he was paying toll, this was what he said, "Thanks, John. By the way, you have a very nice watch. I thought mine was the best, but yours in better! (John laughed so did Tony) And you have a very nice glass!" (he wore a golden glass) John laughed a lot, so did Tony. He was very happy, so was Tony.
* another thing is, actually already mentioned above, when he talks to people, he finds any small thing about that person which he could praise--such as watch, badge, any personal item he has, physical good appearance, internal quality, etc.
* then with that praising, people will become happy, and open their heart, then he will sometimes move into further conversation eventually touching into some deep part of the person.
Anyway, what I observe is that he is always trying to exist for someone's happiness. With this lifestyle, he generates his own happiness as well as happiness of others. Of course he has his own personal challenges, too, but by investing himself into others, it seems that he gains power to go beyond his personal limitation. Someone told me earlier that the living for others is the universal principle. It is a very simple principle but if we live according to that principle, we have ability to generate happiness in any kind of situations.