Comment by shaftway

While I was at Google I was loaned out to the Android team to work on contact synchronizing. There was a problem that I was running into, but it was an extremely rare situation. I pulled aggregated data from production, and it looked like it would affect 0.01% of people. When I presented the solution and mentioned this error rate I was asked how those 200,000 Android users could remediate the situation. They couldn't, their contact sync would just be broken, so I was told to go back to the drawing board.

But yeah, it was the number that was humbling.

There are definitely areas where 4 nines are good enough, but there are just as many areas where the aren't.