Asking this in all seriousness.
A riven that got first blood, got another 2-3 kills in lane... how are you supposed to stop that monster from running down all your turrets?
You can't gank her because you risk heavily giving up a double kill for her.
you need at least 3vs1 to stop that thing, or else she might "outplay" your ass off with all that mobility, shields, cc and raw damage output.
i am standing here asking you, what am i, as a fellow teammate in that game supposed to do?