According to law of probability 50% is true by law itself. The other way to check is to remember three to four major objective events in your life. Go to expert Astrologer with your own horoscope. Tell him either events or years and check how much of it is correct.
Horoscope is with reference to birth time. So past and present have testable ‘future’ value. It can be easily verified. See any Astrologer is ready for this experiment or not?
Most of the people who believe in astrology do not have any knowledge of the structure of astrology. Many of them might have found that some sort of predictions made by astrologers did come true in either their own case or in the case of their acquaintances . That is usually the main reason why they believe in it . Unquestioning belief in age-old traditions is also an important reason. The funny part of this belief is that the predictions that went wrong are ignored or easily forgotten by them. The excuses put up for wrong predictions are commonplace. Pro-astrology people argue that astrologers who have full knowledge of astrology are very rare ; the average astrologers who do not have enough knowledge of it can make wrong predictions ; and moreover , the time of birth provided to them is often incorrect, which makes their predictions go wrong ; but that is no fault of astrology itself ! It is obvious that nobody can eliminate such vague factors, and consequently , real assessment of astrology becomes an impossible task.