Sarah is right, and that probably answered your question. As an addition detail, lawyers are typically allowed to "challenge" potential jurors who they do not want on the jury.
The specific rules for this differ from state to state. In California, where I went to school, there are two types of challenges: "for cause," and "peremptory."
With "for cause" challenges, the lawyer has to convince the judge that there is a legal reason for the juror to be excused. The judge then makes a legal decision whether to excuse that juror.
With "peremptory" challenges, the lawyer does not need to give the judge any reason for excusing a juror. So, these are used strategically by lawyers when there is no "legal" reason (nothing written into the law) to excuse a juror, but the lawyer has reasons they don't want a person on the jury.
The thing is (in California and probably other states), a lawyer is only allowed a limited number of peremptory challenges.
Judges also occasionally excuse jurors who can convince the judge they will suffer extreme hardship if they have to serve jury duty. In a very short trial, these excuses are hard to get.
That may be more than you needed to know, but I thought I'd throw it out there just in case!