Many people think that they can march into court and present whatever document or witness they have to the court. But trial is not that easy. There is an entire Evidence Code designed to stop unreliable information from reaching the ears of the decision maker (either judge or jury). The Evidence Code is meant to provide a level and fair playing field for all parties. If one party was allowed to bring in unauthenticated evidence, then it could skew the truth considerably.
The Evidence Code lays out rules on which every piece of evidence is first authenticated and then presented in court—assuming it can get past hearsay. For example, bank records are hearsay—out of court statements being used to prove the truth of the financial information. To present bank records in court requires they be authenticated by the custodian of records for the bank (which can be done in person or through an affidavit), and then overcoming hearsay by applying the business-records exception. Without those two steps, your banks records will not be admitted as evidence and cannot be considered by the judge or jury at time of trial.
There are times when the opposing party will ask you to stipulate to admit evidence at trial. This can be a helpful tool that allows you and the opposing party to use mutually agreed upon evidence. Bank records are another good example. If both parties want to use bank records, then you can stipulate to their introduction before trial and thereby save yourself the trouble of setting foundation and getting past hearsay. It makes the process much easier and cheaper because you don’t need to serve a trial subpoena on the bank.
Unfortunately, there are times when an opposing party will not stipulate even to evidence favorable to their side. In that event, you pick up the Evidence Code and follow the rules to admit your facts as evidence. It may be a bit more work, but admissible evidence can always be accepted by the Court even over the opposing party’s objection. So when you can’t work it out, use the Evidence Code to your advantage.