What actually goes down
Circuit outages are rarely dramatic. A contractor cuts a line down the street, a provider pushes a bad configuration, an ONT fails, or the local loop degrades until VoIP breaks while web browsing still 'works'.
Once a company runs cloud ERP, Microsoft 365, VoIP and remote access over one circuit, that circuit is the business. Treating it as a single point of failure is a business decision, and it should be made deliberately.