Equivalent trade?

I've always believed in equivalent trade. For example, im nice to you so theoretically u shld be nice to me too. i did smth for you, so i shld at least get back a thank you in return. Yeap, smth like that.

But as i go into the working society, i started realizing that things are not like that. People donte necessary do that kind of thing anymore. What they care about is well, u do smth for them, they benefit from you and thats it.

So anyway, i was about to give up this "equivalent trade" idea when someone at my work place actually gave me a box of donuts. He and his wife cant stop thanking me and kept telling me that i've been of a great help to them. Its really not the donut( not exactly a fan of it), its the sincerity i see in their eyes when they say the thank you.

Hope it make sense.