The Dead Man's Statute
The Dead Man's Statute provides that the verbal statements of a person who is dead or mentally incapacitated cannot be testified to at trial by an interested party.
To put it bluntly, this means that Uncle Harry's deathbed statement to you that it was always his intention to leave you his shopping center is lost to the ages if no one disinterested in his estate (for example, a passing nurse or a visiting unrelated friend not mentioned in his will) was present when it was spoken. Since you were the supposedly intended beneficiary of his generosity, your own testimony to this conversation will not be admissible in a court of law.
The obvious purpose of this law (codified in New York as Civil Practice Law and Rules -CPLR- section 4519) is to prevent unscrupulous witnesses from making up stories which cannot be contradicted by the only other party who was in the room with them at the time because that person is now dead or mentally incompetent. Even though some very legitimate and legally relevant conversations may be excluded from the record by the Dead Man's Statute, every judge and lawyer understands that this principal of law is basically ironclad . On balance, it provides far more protection than it does harm.