1/3 has an infinite nonzero decimal expansion.
Oh, here’s a cute little fact: everyone knows that 1/3=.333333..., right? This means that, by multiplying both sides of this equation by 3, we get 1=.9999999.....
Another way to think of it: if 1 were not equal to .999999..., there would then be some number between the two of them. Since such a number can’t be found, they have to be equal.
Another way: what is the distance between 1 and .999999.....? Since this distance is smaller than any positive number, it has to be zero.