You cannot contest a will simply because you don't like the provisions, or because you received less than you felt you should have received, or because the provisions were, in your opinion, unfair. You must have legal grounds, which, if supported by the evidence, would cause the will to be rejected by the Probate Court.
Lack of Testamentary Capacity
As the question of testamentary capacity applies to wills and will contests, it is often very difficult to disprove. The court presumes that the testator was sane and competent, which means that if you feel the testator was incompetent at the time the will was signed, you have to prove it. This could be quite difficult if the will was signed several years ago, for instance, since it would mean that you would have to produce witnesses and other evidence relating to the specific time the testator signed his will. And remember that eccentricities are not necessarily indicative of incompetence or lack of understanding, and that persons who are suspected of being incompetent can have moments of lucidity, so that even credible evidence of weird behavior and occasional incompetence may not be enough to support a will contest based on lack of testamentary capacity. And if the will was signed in a lawyer's office, you have an even slimmer chance of proving lack of capacity, because most attorneys are extremely careful in monitoring the signing of the will, which normally includes a brief discussion with the testator to satisfy the witnesses that he knows and understands what he is signing.
Assuming there is some substance to the claim, this may not be quite as difficult to prove as lack of testamentary capacity, since it goes to the actual facts and circumstances surrounding the signing, as opposed to an evaluation of the state of mind of the deceased from a distance. If it can be shown that any of the necessary requirements was missing, the will may be declared invalid and the contest successful. As noted above, however, if the will was signed in a lawyer's office, the chances of proving improper execution are slim. But many testators (to the delight of the many lawyers who are paid to contest wills) write their own wills and also arrange for the signing and witnessing. Such cases are the ones most likely to sidestep an important legal requirement.
A bogus or inauthentic will generally involves fraud and, like certain other grounds for contest, overlaps with it. An illustration is a will that was rejected as not being the will of deceased. The same would apply, for instance, where the will was originally that of the deceased but someone made an unauthorized change to it, then offered it for probate. This method can be quite difficult to detect, since, in most cases, the will was properly signed by the testator and witnessed according to law. But as is often the case, those stealing from the dead are usually amateur thieves and don't cover their tracks very well.