It is a very easy thing to tell someone what they should do, rather than having to worry about actually setting the example yourself, because setting the example yourself, actually requires that your words match your actions. That is to say, when you tell someone that they need to be more polite, or more generous, or not to curse, or to control their temper better, that is all fine and good, for these qualities in a person are good qualities to have, but those words will go a heck of a lot further when they come from someone that demonstrates consistently that they personify those very same attributes that they wish the other person to follow.
It simply isn't good enough to demand or instruct someone else how they can be better, if you are unable to exhibit those same qualities in yourself, for though the advice may be good, that advice is also hollow. Now, it could be that the advice is presented in a way, in which one person says to the other, "please, don't drink, for I do, it has ruined my life and I can't seem to quit it," for at least there is pathos and honesty there, so that, the admission that is made from the one giving the advice is doing so from their personal experience, in which they have fallen victim to a particularly bad vice, and do not wish to see their error, compounded in another. This then, is sound advice in which the person giving it, freely admits their weakness and tries to encourage someone else not to develop that same habit for the evident results are not desirable.
Then, there are those that consider themselves to be angels in disguise, and though there are indeed some that rightly fit this description, most people that believe this, really are not, so that their self-righteous way of instructing and correcting others, grates on another person's nerves, so that, almost out of rebellious spite, the other person that may not have been thinking about doing something that they know they really shouldn't, may find this somewhat more alluring, simply because a pompous ass is trying to instruct them otherwise.
The words that we speak are a valid and necessary form of communication, but words are not the only form of communication that we have, and those that do not understand that words and actions should actually align with each other, misunderstand this importance, because way too many people, actually know what is right, but somehow or other aren't able to actually do right, in which that failure and inconsistency is actually the visible story that is being told.
The fact that so many people know right and do wrong, indicates that proper character development is something that far too many people fall short of, in which, if there were more people that actually set a good example by living a good example, the overall result for society would be a vast improvement in character, because we are what we do and accomplish, and we learn best from those that have demonstrated such in a virtuous way, of which, apparently they are in rather short supply.