I think it's something like this.
0.9999... Isn't one, if it was one, it would be 1.
It is however a very close approximation of one.
It is not one simply because there is ALWAYS a remainder.
Add 0.0001 to 0.9999 and you get 1 just as if it were to any decimal point or infinity.
Factually, accurately 0.9999... Will never and can never be one it can only be approximated to be one. Imo.