It could be that you have a friend or relative who was arrested on DUI charges in circumstances similar to yours. Perhaps the outcome was good, so you think yours will probably be too. Or maybe the outcome of that case was negative, so you feel discouraged about your chances.
Here is a word of advice: Do not let your friend's case, good or bad, influence how you feel about yours because each situation is unique. Even if what you see as the important particulars are the same, chances are there are nuances you have not thought of and that can greatly affect the case.
For one thing, you and your friend are different people with different personalities. You are likely to come across differently to lawyers and judges, and if applicable, on the witness stand. It is also probable that your case and your friend's involve different city and state laws, police officers, lawyers and judges. A DUI charge in the Denver area can play out very differently from one in Memphis. A lawyer well-versed in DUI law and who has in-depth experience working with prosecutors and judges in one area may fare better than a new-to-town lawyer or one who does not do traffic-type work.
The facts of the case
One reason why the choice of lawyers is important is because it lets you, to a certain degree, better understand your case and take control of it. For example, say that your friend was able to get off because the police officer incorrectly administered the breath test. Maybe you decide to represent yourself and use that same argument. Only, in your case, you are unable to come up with evidence to back your claim of a faulty breath test. It could be that you have several potentially productive lines to explore such as being wrongly pulled over or an uneven road, but someone in your corner needs to be able to review these facts and understand how to present them.
The bottom line is that each DUI case is different. Even an officer pulling you over one street away from where your friend was can be significant or having taken medication for the first time before driving could become an issue.