It is typically very difficult to challenge a will. Wills are seen by the court as the voice of the testator, the person who wrote the will. Since that person is no longer here to speak about his or her wishes, the courts stick pretty stringently to the will. Anyone who may have an interest to gain from the will can challenge a will. The most successful challengers are usually the spouses, and the most successful grounds are that the person lacked testamentary capacity or that the person was unduly influenced or persuaded to write the will a certain way. Adults are presumed to have testamentary capacity and in order to challenge a will based on mental capacity, you must show that the testator did not understand the consequences of making the will at the time of the will's creation.