It may not be as obvious as all that. I knew an old lady who used to visit every new solicitor who opened an office in her area, and made a new will each time. Different dispositions, different executors, etc., each time. When she died, her daughter took all the wills to the probate office , who said they were too confusing, and declared her intestate. Bear in mind, all these wills had been drawn up by qualified solicitors. Presumably each solicitor thought each will was valid. Seems they were all wrong.