To do your very best as a defense lawyer you must be guided by a strong desire to serve the constitution. Clients need your help to understand the criminal justice system and how it will affect their case.
The vast majority of people who find themselves in criminal court have never been there, and never will again. Many of them make decisions about their case without ever talking to a lawyer. Those decisions often have an enormous impact on their personal and professional lives.
Much of what a good lawyer does is educate his client, prepare them for the choices they face, and help them make an informed, deliberate decision. This aspect of criminal defense can be very rewarding because it affords the attorney the chance to educate, inform and protect his client all at the same time.