The only way to live in this wicked world is to be assertive and ignore our neighbours
If we are assertive and we ignore our friend's problems, they surely won't help us when we'll be in need. Of course I don't mean that favours are acceptable only when they are profitable.
I think that assertiveness is a good feature as long as it's not altering into selfishness. It is for people who do not know how to say NO, but it does not mean a person should answer NO to every single question, he is asked.
For ages kindliness and disinterestedness have been the most valuable features of human characters. Those traits have been always used in films for children and people who are endowed with them always win with the evil, so maybe it pays to be kind
It is very difficult to draw the line between being kind and assertive and being an ignorant. We have to learn to distinguish those two ways of living and hopefully then our existence in this world will become more enjoyable and easier.