When a person consistently has a perception of what is true and lives it, he gains a force of beauty of character. In other words, faithfulness creates favorable impressions that open doors for him.
For example, to whom would we rather loan money, to a person with a record of steady work and payment of debts or to one who cannot keep a job and consistently defaults on his obligations? Which one is more likely to get the loan? A person of good character recognizes his responsibility to truth, understands it, and submits to it. This produces the witness that glorifies God.
If a person will not follow this process, he will not have the good character and the good name to go with it. If he recognizes and understands his problem but does not submit to the truth, he is deceiving himself.
This principle holds true in every area in which a name is built, including marriage, childrearing, and health issues. Many run from the truth about themselves. Hardly anything will destroy a reputation quicker than for others to know an individual is lying to himself about what or how much he eats, his failure to discipline his children properly, or his careless inattention to his spouse. Such faithlessness provides a strong foundation for hypocrisy.
The ninth commandment not only covers bearing false witness verbally, but also bearing false witness about one's relationship with God by displaying a spotty example of conduct, all the while claiming to be Christian. To make a bad witness in ignorance or weakness is one thing, but to know better and deliberately mislead is another matter altogether.
Why do we lie? Often, it is to cover up our irresponsibility. We fear that something about ourselves we wish to keep hidden will be exposed, so we lie to protect the image we want others to see. We also lie to rise above our feelings of inadequacy or inferiority. We also do it to lower a third party in the eyes of others, which, of course, has the effect of elevating ourselves in our own eyes and, we hope, in the eyes of others.