Answer:
Your first flip has a 1/2 or 50% chance of getting tails. In order to get 2 tails in a row you have to get tails first and then again. The first flip is 1/2 and the second one is another 1/2. Combined you have a 1/4 chance of getting 2 tails in a row.
Each time you flip you have 1/2 a chance, but when you look at all the flips at once, each consecutive flip of the same side has a smaller probability.
