therefore it's 1/14 cause there are 7 days with 50% chance.....just saying....
Actually if we make the presumption that there WILL be a trailer BEFORE the game is released there's a 1/1 (100%) chance there will be a trailer before the 17th.
Looking at each day individually there's two options: either there will be a trailer or not - so that's a 1/2 (50%) chance.
Looking at which day it will be released there is a 1/6 chance for any given day.
My point is your grasp of probability theory is wrong sorry. 1/14 would mean that for instance: A throw of a 14-sided dice like people could use in traditional RPGs.
The reason this situation is not 1/14 is because you know there's only ONE possible outcome (trailer being released) which you know will happen, the sample space is now 6 different days = 1/6 (or 1/7 when you made your post)