The biggest disadvantage of writing your own will is that you will not have professional legal advice from a trained expert. Attorneys know the state laws for writing a will, and they can advise you on how to ensure your will is legally valid and less likely to be contested by your heirs. An attorney can also help you make sure your will is comprehensive enough to include everything necessary to provide full protection for your loved ones. Without an attorney, it's possible your will won't be valid, that your heirs will challenge it, or that you will be missing clauses you need such as provisions detailing who should manage the assets left to minors.