It's just superficial. Speaking and doing things must be beneficial to yourself. The key is how do you understand "interest"

For example, a stranger in the station asked you to look after ta's luggage, and you said, "Give me the money, or I won't do it." This is the most direct benefit. I don't do anything without money.

For example, if you see someone stealing a wallet on the bus, do you want to shout? Helping others can be appreciated by everyone, and you can also make yourself excellent, and then you will be happy. Is this an interest?

-Buy gifts for boyfriend and girlfriend in love to make ta happy. Is it good for you here?

-Help mom and dad do what they can. Is it good for you?

There are many interests. Money, friendship, affection, happiness and study are also good for you, because you can make yourself excellent and earn a lot of money in the future. These are all good things for you, depending on what you think.