A case in point:
On this day in 138AD the Roman Emperor Hadrian named Antoninus Pius as his successor. Later that year, Hadrian died of natural causes, and Antoninus reigned for the next 23 years. Antoninus is still remembered as one of the few "good" Emperors and had a mostly peaceful reign, dying of old age in 161AD, leaving Rome to his successor Marcus Aurelius (mostly known today for being played by Richard Harris in the movie Gladiator).
ON THE OTHER HAND:
On this day in 50AD, the Roman Emperor Claudius named Nero, the 14-year old son of his third wife, Agrippina, as his successor. Four year later Claudius died, poisoned by Agrippina, according to Tacitus. Nero ascended to the throne, killing Brittanicus, Claudius' son by his second wife and later (again according to Tacitus) his own mother, Agrippina. Nero became one of Rome's most despised Emperors and was removed by a rebellion in 68AD in which he committed suicide.
SO, CHOOSE WISELY: