If I myself am not perfectly able to do what a philosophy suggests/ demands of me, who am I to say "go and do (or avoid) such and so?" Or is this a philosophy of "Do as I say, not as I do?"
Let's suppose there's a moral rule:
Moral Rule Always be honest.
Further let's say there's a good argument for Moral Rule, maybe it goes like this:
1.) If we are not required to be honest at all times, it might be permissible to make other people worse off who don't deserve it. 2.) It could never be permissible to make other people worse off who don't deserve it. 3.) Therefore, it is false that we are not required to be honest at all times.
Always be honest.
Now if I say we should all follow Moral Rule, and you point out that I wasn't honest once, you haven't given any reason whatsoever to show that Moral Rule is false. You've just given a reason to think that I personally am not a perfect person, but my inability to follow Moral Rule doesn't provide any evidence whatsoever that premises (1) or (2) above is false, nor does it provide any reason to think (3) doesn't follow from them.
In general, the reasons to believe the moral rule are what they are impersonally, regardless of the character of the people who think moral rule is true (or false, for that matter.)
Imagine the analogous case with mathematics. You would never tell your calculus professor that you didn't have to listen to the fundamental theorem of calculus because you saw the professor cheating on his spouse. To do so would just be absurd---the professor's character has nothing to do with the reasons to believe the law correct. (Although it may have everything to do with your evaluation of the professor as a person.)
As shane said if a rule is derived as the best then only the striving for it with the hope of achieving is what matters. Like an ideal for athletes.
Although very hardly can we be certain that an ultimate law of life can be derived without first experiencing it and then realizing it. You can see that among people that live in very demanding environments where every choice and action counts: when you tell them what someone proposed they ask you about his past.
This has been a tragic part of philosophy for a very long time and maybe you agree that a huge part of religious texts, idealistic writting and of the romantic era are hugely mistaken. People that wanted to 'derive' laws instead of exploring and looking for them in life have made those mistakes. We should be more sceptic about laws and more interested in method and values.
The real question is how do you know that a rule is true? Is it just a guess or a fact? Is it a guess of the immidiate future or the long term? Every guess that reaches too far is destined to fail, as in meteorology (5-day limit). Is it a generalization or for specific cases?
For the specifics of human justice that is crucial for everyone and very often we are asked our opinion of it I like this quote very much 'justice is the intelligence of the human'.
What everyone needs to understand about philosophical positionings, of any caliber, is that living the philosophy is a journey, not a destination.
Therefore there is no ''Do as I say, not as I do''. It is more realistically; ''Do as I am endeavoring to do, not as I am attempting to tell you to do.''
The ''do as I say, not as I do'' axiom, is preschooleresque in its conceptualization, and below the contempt of individuals with more high-schooleresque intelligence.