That's the exact saying my professor was telling me today! :D
If everyone had the "don't help anyone" mentality then the world would be a very miserable place. Imagine where we would be if noone helped another, humans are an interdependent species, we can't thrive or progress on our own, we need eachother. That's the bottom line. So help whenever u can without expecting anything in return, and one day when u really need the help u'll find someone there for u.

I'm not always right, but I'm never wrong :P - Garfield