Short version, two coin flips. There are 4 options:
HH, HT, TH, TT
So there’s two chances to get one Tails and one Heads, out of 4, so 2/4 = 1/2, half the tosses. Then 1/4 on each of HH and TT.
So rolling one Tails is more likely than rolling two.
But once you’ve flipped the first coin, it’s “locked in”. If it was Heads, the only options left to you are HT and HH. The fact that there could have been a T that, if flipped first, would land us in TH is irrelevant fantasy. We’ve got the H, and all that’s left is HT or HH, even odds.
Dice are the same. What makes a double 1 rare is that you have to roll 1 specifically and only two times to get there, whereas a single 1 can be first or second, and the other number can be any of the other 19 other numbers. It’s the duplication of different results we consider “the same” that make one thing more likely. But once you’ve already rolled a 1, none of that matters anymore. Now it’s just 20 numbers, each equally likely. We’re locked in.
Short version, two coin flips. There are 4 options:
HH, HT, TH, TT
So there’s two chances to get one Tails and one Heads, out of 4, so 2/4 = 1/2, half the tosses. Then 1/4 on each of HH and TT.
So rolling one Tails is more likely than rolling two.
But once you’ve flipped the first coin, it’s “locked in”. If it was Heads, the only options left to you are HT and HH. The fact that there could have been a T that, if flipped first, would land us in TH is irrelevant fantasy. We’ve got the H, and all that’s left is HT or HH, even odds.
Dice are the same. What makes a double 1 rare is that you have to roll 1 specifically and only two times to get there, whereas a single 1 can be first or second, and the other number can be any of the other 19 other numbers. It’s the duplication of different results we consider “the same” that make one thing more likely. But once you’ve already rolled a 1, none of that matters anymore. Now it’s just 20 numbers, each equally likely. We’re locked in.