I do feel like I don't receive the same treatment as some of the others. I am old enough to know that it is part of life and I am used to it. I am wondering why the giver gives to some people but not others. What is the psychology behind it?

The coworker I mentioned, we work side-by-side, deal with the same people. Why does she receive special gifts from clients and I don't? Besides getting paid by the hour, she gets gifts. It's not that I want the gifts, I can buy things for myself, but what am I chopped liver?