There is both good and disaster with single sign on. We use SSO at work all of the time. But, at work, we are behind firewalls (several in fact), some servers and systems are only local with no internet access and others are global systems. But, like I said, all are behind overly secure firewalls because they are pharma and just can't have a breach. But these personal SSOs .... well, therein lies a huge issue which I think your image points out. If you use SSO for 2 or more things, once your compromised, the attacker has access to everything. Your world could turn into a nightmare in less than 5 minutes. But sure, some are turning to 2 factor authentication now ... but, that only really works if it stores your IP address and doesn't recognize the device you're on (which I'm not sure all do). But, if it's got your IP address, does that make it worse?