If I kiss you, that is a psychological interaction. On the
other hand, if I hit you over the head with a brick, that is also
a psychological interaction. The difference is that one is
friendly and the other is not so friendly. The crucial point is if
you can tell which is which.
It is generally agreed that "Hello" is an appropriate greeting
because if you entered a room and said "Goodbye," it could confuse
a lot of people.
Receiving a million dollars tax free will make you feel better
than being flat broke and having a stomach ache.