Suppose a random person comes up to you and says "Think of a number between 1 and 10." You think of one. He guesses it correctly. You seem slightly surprised but ask him to do it again. He does it again. He ends up doing this successfully six straight times. Let's call your degree of belief in him using his mind to successfully guess your number d. You are apriori an ardent skeptic and believe that psychic abilities are a scam but your d has now gone significantly up.
Now, suppose you learn that he had been doing this to people for a year. Every single day, he'd go up to ten people and try to guess what number the other person is thinking of. Your degree of belief d changes. In fact, it becomes very minimal if not nonexistent.
And yet, on that day, it wouldn't have mattered if he did this to 50 other people, 10,000 other people, or 10 million. The probability of him guessing your number 6 straight times was 1 in 10^6 either way.
Is it rational to change your degree of belief in something depending on how many opportunities of an event there were in the past? Many would say yes, but this introduces a new problem: what defines an opportunity? In this case, should an opportunity only consist of how many times that person guessed a number before? What about how many times that person made other sorts of predictions? What about how many times other people made predictions? What about how many times opportunities arose for a meaningful event to occur, such as finding a lost friend after a year? How do we differentiate these classes?