Most of us don't spend much time thinking about the Bill of Rights and what it stands for -- at least, we don't until one of those rights is imperiled.
One of the most important rights enshrined in the U.S. Constitution is the Sixth Amendment's guarantee of your right to an attorney. The Founders who wrote the Bill of Rights recognized that a person charged with a crime has little chance of receiving a fair trial if they are forced to defend themselves in court. It was just as true then as it is today that your only realistic chance of avoiding jail time is to have an experienced defense lawyer representing you.
How the right to counsel has grown
It is important to remember that the Sixth Amendment's "assistance of counsel" clause was pretty limited in application for many years. For more than 170 years, it only applied to people charged with a federal crime. It wasn't until 1963, in the landmark Gideon v. Wainwright, that the U.S. Supreme Court ruled that the right to an attorney also applied to state felony charges.
Cost was a separate issue. Many people accused of a crime cannot afford an attorney. Fortunately, the Court also ruled in Gideon that the government must provide competent legal counsel to all defendants facing a felony charge. In 1972, the Court went further. It found in Argersinger v. Hamlin that defendants have a right to counsel, regardless of ability to pay, any time they are facing possible imprisonment.
The right that protects all your other rights
If you have been charged with DUI or any other crime, you have several rights. But virtually the only way to protect those rights and level the playing field against the prosecution is to invoke your right to a defense attorney.