I would say sometimes they get caught up with their own ideals, whereas not everybody thinks the same way so what is normal, good and expected is what causes the other person to be naive and act in a reverse manner, against the "advice".

There was a great "quote" from the "KOTOR(Knights of the Old Republic (Star Wars RPG game by BioWare)"
where you as the main character disembark your ship, enter some slums and get cut off by some "homeless" character asking for some credits (little do you know there is a tough lesson ahead) as with all RPG's there are many options but one in particular is very revealing of the above "rule":

If you choose to give him credits, he thanks you, you get good points and after a second you see him with the thanks of your "master" the "old and wise granny" how he gets beaten up for his money and left in the gutters with nothing, from then on I was thinking how in most cases when you help somebody you are helping yourself, so you aren't really helping anybody but yourself, since the other person has to solve his problem, if you step in he won't gain the "xp" knowledge/resilience ad you will gain all the credit.

On a related topic is also the kind of people that never ask for help, now there I think you should help when necessary since they might end up seriously harming themselves, think of somebody in the GYM trying to lift, without proper form and previous preparation(rigorous training) well if you don't help him he might end up crushing his skull, or breaking his back doing some deadlifts, just because he decided to do something and tried his hardest past his real limit (limits get pushed gradually).

So far so good, good evening and good luck :)