Usually, it's not what's in your estate planning documents that is a problem. On the contrary, it's what's NOT in your documents. If you want something to occur, whether it's a health care matter or how your estate will distribute upon your death, you should make sure you spell things out clearly in your documents.
Life is unpredictable. As a general rule, how you think things will unfold is not necessarily how things will unfold. If you've lived long enough, you know that's true. Therefore, if you something specific to occur with your estate or with anything involving your estate plan, the best course of action is to spell things out clearly. For example, if you don't want your children inheriting everything from you right away, then spell it out. How exactly do you want them inheriting from you? What can they use the money for? When don't they inherit from you? What if they are in the middle of a divorce? What if they are in the middle of a bankruptcy? What if they have a substance abuse problem?
With respect to health care decisions, who will be in charge of those decisions? Do you want extraordinary measure to keep you alive and breathing or do you prefer quality of life over quantity of life? When it comes to estate planning, the more you leave to the imagination the more likely there are going to be problems. If your kids are fighting over what to do with your real estate upon your death, wouldn't it be nice if there were some instructions about that issue in your living trust? If you anticipate certain issues are going to occur, the best thing to do is "spell out" your wishes clearly and without ambiguity. If you are choosing trustees, executors, agents, and others that you truly trust, then perhaps you should give them the discretion to act according to your wishes.
Again, being clear in your estate planning documents is much better than being unclear. Don't leave these things to chance. You've spent your whole life building up your estate. Why should you squander it all away by improper or inadequate planning? Remember, it's not just about who inherits from you. It's about what will happen if you can no longer act on your own behalf. A good estate plan not only addresses you gets your "stuff" when you die. It's more about who has the legal authority to act on your behalf and if you've given them the proper road map to do so.