The reason is different than you think.
Most people who have not gone through the litigation process think that there's something wrong with an attorney preparing the client for their deposition. They think somehow that the attorney gives the client the answers to questions. Nothing could be further from the truth.
The reality is that the preparation process is to give you, the injured victim and understanding of what types of questions you will be asked by the attorney who represents the people you have sued. It also gives you an opportunity to refresh your memory about the events that occurred, most likely many months or years before.
Most injured victims try and put out of their mind the painful details that occurred when they were injured. They have been trying to recuperate and get on with their lives. They may not remember many of the finer details that occurred in and around the time of their incident.
When you are prepared for your deposition, your attorney will explain how the process works and give you examples of questions that the defense attorney will likely ask. Your lawyer will explain the basic ground rules and what to do if you do not remember or don't know the answer to a question.
I always tell my clients that a pretrial deposition is nothing more than a question and answer session, given under oath. If you do not know the answer to a question, you simply tell the attorney “I don't know.” It is not a guessing game and it is not a test. It is simply your ability to remember certain facts that occurred a long time ago.
Did you know that an attorney is obligated to prepare his client for pretrial testimony and also for trial? It's true. A lawyer who fails to live up to that obligation is doing his client a serious disservice. Did you know that this happens not only with the injured victim who testifies, but also the defendants- the people you have sued?