After reading the biographies of U.S. Supreme Court Justices, it is clear that most of them have gained experiences in both private and public arena. A significant number of judges engaged in private practices before entering the civil service career. Many Justices have also served as special assistant to former judges or as counsels to state and/or federal governments. Some were assistant attorney generals and others spent few years in the academia. Thus, most of the U.S. Supreme Court Justices have been exposed to both academia and real-world practice.
Even before reading the biography, I had known about some of the Justices before due to a number of major cases in the U.S. Supreme Court in recent years. I could not help but notice that U.S. Presidents tend to nominate Justices for Supreme Court who share similar ideologies as the Presidents themselves. For example, conservative judges such as Justice Scalia, Justice Thomas, and Justice Roberts were nominated by Republican Presidents while relatively liberal Justices such as Justice Kagan, Justice Ginsburg, and Justice Sotomayor were nominated by Democratic Presidents. I believe Justices should be able to rise above their personal beliefs and some of the U.S. Supreme Court Justices have disappointed me in this regard.
This is why I am against lifetime appointments and instead believe in one long non-renewable term such as of 15-20 years. Another trend I could not ignore is that there have been efforts in recent decades to compose more diverse body of Justices. Now there is one African American Justice and three women Justices which is a step in the right direction.