A lot of us are taught to spare other people's feelings & in no other way is their more evident than when someone ask us to do something we dont want to. Often we will allow ourselves to go along with it just to avoid an awkward situation or to save the other person from feeling uncomfortable.
In this process , we make martyrs of ourselves & chip away our own self esteem .
I am not saying you should never help the one who really needs you, but sometimes it is important to learn to say NO . It will free us from unnecessary burdens, prove how much strength we really have & make us feel good about ourself. :)