>What takes the long amount of time and the way to think about it is that it’s a march of nines. Every single nine is a constant amount of work. Every single nine is the same amount of work. When you get a demo and something works 90% of the time, that’s just the first nine. Then you need the second nine, a third nine, a fourth nine, a fifth nine. While I was at Tesla for five years or so, we went through maybe three…
Ha, I often speak of doing the first 90% of the work, and then moving on to the following 90% of the work...
— Tom Cargill, Bell Labs (September 1985)