Very few wills are ever challenged in court. When they are, it's usually by a close relative who feels somehow cheated out of a share of the deceased person's property. To get an entire will invalidated, someone must go to court and prove that it suffers from a fatal flaw: the signature was forged, you weren't of sound mind when you made the will, or you were unduly influenced by someone.
For more information on how a will can be challenged in court, see Grounds for Challenging a Will.
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