When a person creates a will, it is very important to establish his or her testamentary capacity for the will to withstand potential legal challenges. Testamentary capacity is a person's legal ability to create a valid will. Some individuals simply do not possess that capacity. For instance, in most cases, a legal minor under the age of 18 cannot legally create his or her own will.
In most cases, testamentary capacity comes under scrutiny when an interested party suspects that the testator created the will under the influence of drugs or coercion or was otherwise mentally compromised. If, for instance, the testator creates the will while he or she is not mentally sound due to the effects of the sickness and accompanying medication, then the testator probably does not have testamentary capacity.
Even if a person is of sound mind, generally speaking, he or she may not possess testamentary capacity in certain circumstances. This is worth considering if you suspect that some other party placed undue influence on the testator to write in certain provisions, using blackmail leverage or other means, then it is worth considering a challenge to the will on the grounds of coercion.
There are many ways to compromise a person's ability to create a will. Whether you have concerns about the validity of your own will or suspect that some other party had inappropriate involvement or influence during a will's creation, it is wise to review these issues very carefully in the eyes of the law. Be sure to look at these matters very carefully to keep your rights secure and resolve the distribution of an estate fairly.
Source: FindLaw, "Reasons to Challenge a Will," accessed June 08, 2018