When you create a trust, it is important to think about the unexpected -- about the things that may happen that you cannot predict. You do not want to accidentally keep money from your heirs when you would have preferred to pass it on to them. You can't change the trust after you pass away, so you must plan for all possible outcomes in advance.
One question that the court may ask when determining the validity of a will is if the person who did the estate planning possessed the testamentary capacity to do so. It's very important to understand what this means and how it can impact an estate plan.