It is not impossible. Think about it. Although the monkeys would have to hit the exact keys, and avoid the backspace, they are not thinking. It is dumb luck. The odds would be something like 1 in 1,000,000,000,000,000 to the power of twenty million times that number, but the fact is that it is INFINITE. That means forever and ever. Never stopping. Eventually the odds of getting it will be surpassed by the years, multi trillions of times. It never stops. Of course it's possible. Heck it would happen an infinite amount of times.
From other board.
Also, would like to add. The probability is not impossible. Therefore, no matter how small the odds it will happen.
I believe somewhere in this long explanation is the answer!