"Keep in mind that everybody is a mutant!"
No, this is not about the X-men. No, this is not the same as "We all have sins" or "Nobody is perfect", cliches that are void of real meanings but help make excuses. And it is not about people being different. We can be different, like in skin colors or blood types, but certainly still normal in those aspects.
This fifth commandment has a long line of solid scientific findings backing it up. While we'd like to think that bad things, like AIDS, cancers, accidents, happen to everybody but ourselves, the reality is that bad things are of equal opportunities. If there is an angel, or a model human genome with every nucleotide of its DNA is "perfect", and if we compare our genomes to it, we will find none of us is as good. A recent paper provides the most evidence thus far: A Systematic Survey of Loss-of-Function Variants in Human Protein-Coding Genes, 2012 Science 335: 823-828. They found that all the sequenced human genomes contain a large number of variants that are predicted to inactivate protein-encoding genes. On average, every person has ~ 20 genes (out of ~ 20,000 in total) that are completely inactivated. If we look at the many known mechanisms that can kill gene expression beyond the DNA level, the list of "dead" genes is likely much higher. There is no wonder that more and more medical problems are being discovered and the incidents of known diseases are going up, as our knowledge and technical tools are getting better and better.
What can we do about it? This is the real question, because for various reasons we can't simply correct our DNA mistakes easily or early enough. We just have to accept the fact that we all have specific problems others don't, and that such problems are mostly due to genetics beyond our control. Luckily, most problems are minor and appear in only limited situations. But genetics goes a long way to explain why everybody behaves in an idiosyncratic way, consciously and subconsciously.
Genetics not only influences individuals, it also affects societies, simply ensembles of people and many genomes. Societies determine to a large extent how individuals see things and think. So to take this commandment to a higher level, every society is also a mutant, even if not entirely due to genetics. Many things in a society are not "perfect", including rules that have been around for thousands of years.
As a corollary, be critical towards ourselves and towards the societies. Don't take anything for granted. And we have to constantly and actively suppress the effects of mutant genes and their consequences. Just like an HIV-infected patient. The current treatment suppresses but does not eliminate the virus, and you need to take the pills consistently. For many of the ills at the individual and societal levels, we have to do the same. A glaring example is racism. Everybody has racist tendency, because it is simply rooted in evolution. All organisms like to be around the alike, wolves, horses, etc. Human ancestors needed to group together to fight wild animals as well as other tribes. This was how friends and foes are recognized for billions of years. In modern societies human skin color is no longer defining friends and foes or good and bad, but part of our genes and brains are still wired to such and other prejudices. This is something one needs to actively fight to suppress every day, no matter he is white, black, yellow, or brown. Very often we see people violate this "rule". It is likely because they forget to take their HIV pills.
As the last note, the skin color in some societies still predicts economic status. Who doesn't want to be that gorgeous person with well-tailored dress and designer shoes riding in expensive cars to dine at fancy restaurants? Such a person is also often perceived to be nobler than a poor guy. Here is an interesting paper looking at the morality of people of different social classes: Higher social class predicts increased unethical behavior, 2012, PNAS 109: 4086-4091. In essence, with numerous tests and real, hard data, this paper demonstrates that upper-class individuals are more likely to break the law or engage in unethical acts than the lower-class individuals, given the same chances. Don't paint everybody with a big brush, but we do need to think what lies beneath the glamorous looks. Because judging a person by his look or outside attributes is also a common human fallacy.