From Chanakyaneethi

Be content with what you have already got as wife, food and income. But don’t ever be content with your knowledge, self-improvement and charity.... Chanakyaneethi

There is some self-interest behind every friendship. There is no Friendship without self-interests. This is a bitter truth...... Chanakyaneethi

(In this context something else comes to my mind. I read somewhere that 'People are greatful to you for NOT what you have done in the past, but what you can do for them in the future'. Many a time we forget this and comment how a particular person has been ungrateful to you despite you helping him in the past.)