8 Answers

I was always taught to stand back and let other people go first, but nine times out of ten I have found when you do that people will walk all over you, and you get left standing there. So yes I think it is true.

If not being assertive enough means your a nice guy, you will finish last.

Yes, it seems to be true but, I'll bet the "nice" people are happier.............

Uhhhhhh .... Hmmmmm ..... I'll come back with an answer later. 

They finish in top 5 and rarely last

Not always.  Sometimes, certainly, because a "nice" person may defer to someone less deserving.  Other times, it's just easier to avoid a confrontation by acquiescing to the nasty person and letting "karma" work its magic.  Sometimes the "bad guy" never loses and appears to be an unequivocally happy person; I think somewhere there is a roiling fire burning a hole in that person's gut. 
Nice guys / girls finish last.....sometimes, but not every time. 

Yes.

Jimmy Carter.  Dead last.

No...There`s a difference between being nice and being a total door mat!....It`s a balance be nice but be assertive!!:+)