A good way of thinking about this is by looking at the ratio of odd numbers to even numbers when you start counting from 1.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
No matter how long you count, you'll find that at any given point, one of two things will be true:
•You've touched more odd numbers than even numbers
•You've touched an equal amount of odd numbers and even numbers
What will never happen, is this:
•You've touched more even numbers than odd numbers.
Similarly, consider a coin, launched in the "heads" position, flipping heads over tails through the ether:
H T H T H T H T H T H T H T H T H T H T H T H T H
At any given point in time, either the coin will have spent equal time in the Heads and Tails states, or it will have spent more time in the Heads state. In the aggregate, it's slightly more likely that the coin shows Heads at a given point in time—including whatever time the coin is caught. And vice-versa if you start the coin-flip from the Tails position.
上述都是把還沒丟時的那一次列入選項，若未丟時這次不能納入
變成了
T H T H T H T H T H T H T H T H T H T H T H T HT