1. The fine-tuning of the universe is due to either physical necessity, chance, or design.
2. It is not due to physical necessity or chance.
3. Therefore, it is due to design.
Sometimes skeptics will offer a lottery example in order to justify the chance alternative. In his book On Guard, William Lane Craig illustrates how this claim might sound:
"In a lottery where all the tickets are sold, it's fantastically improbable that any one person should win, yet somebody has to win! It would be unjustified for the winner, whoever he may be, to say, 'The odds against my winning were twenty million to one. And yet I won! The lottery must have been rigged!'
In the same way, they say, some universe out of the range of possible universes has to exist. The winner of the universe lottery would also be unjustified to think that because his universe exists, this must have been the result of design, not chance. All the universes are equally improbable, but one of them, by chance, has to win." 
Dr. Craig goes on to explain why the above analogy betrays a misunderstanding of the design argument:
"Contrary to popular impression, the argument for design is not trying to explain why this particular universe exists. Rather, it's trying to explain why a life-permitting universe exists. The lottery analogy was misconceived because it focused on why a particular person won.
The correct analogy would be a lottery in which billions and billions and billions of white ping-pong balls were mixed together with just one black ping-pong ball, and you were told that one ball will be randomly selected out of the horde. If it's black, you'll be allowed to live; if it's white, you'll be shot.
Now notice that any particular ball that is randomly selected is equally improbable: No matter which ball rolls down the chute, the odds against that particular ball are fantastically improbable. But some ball must roll down the chute. This is the point illustrated by the first lottery analogy. That point, however, is irrelevant because we're not trying to explain why this particular ball was picked.
The crucial point is that whichever ball rolls down the chute, it is overwhelmingly more probable that it will be white rather than black. Getting the black ball is no more improbable than getting any particular white ball. But it is incomprehensibly more probable that you will get a white ball instead of a black one. So if the black ball rolls down the chute, you certainly should suspect that the lottery was rigged to let you live.
So in the correct analogy, we're not interested in why you got the particular ball you did. Rather we're puzzled by why, against overwhelming odds, you got a life-permitting ball rather than a life-prohibiting ball. That question is just not addressed by saying, 'Well, some ball had to be picked!'
In the same way, some universe has to exist, but whichever universe exists, it is incomprehensibly more probable that it will be life-prohibiting rather than life-permitting. So we still need some explanation why a life-permitting universe exists." 
Courage and Godspeed,
1. William Lane Craig, On Guard, p. 114.
2. Ibid., 114-116.