@wronglang @stefano @david_chisnall adding complexity. And the high scale system is complex enough that you only get reliability if top executives consistently value it year over year. Source: I worked at a place that was 5 9s for many years and a place that went from 2 1/2 nines to to about 4 1/2 nines over fifteen years or so. Someone responsible for reliability has to be able to say roll back to teams with bad code and it has to stick. Plus honest incident review and continuous improvement.