The grandparent poster's point is if you played "over a dozen", say, 16 games and one of them failed, then 93.75% of games worked for you. Getting to 99.9% requires a lot more games to succeed for even a single failure.
Obviously in context you didn't literally mean 99.9%
Ah OK got it, you're right it was more "they/it/Steam work/works for me" not a scientific assessment, thanks. The percentage was supposed to be like witty or something. My system isn't even a serious gamer machine, cost like $1200 last year.