[riobard]

This is the beauty of aggregation: when you add a lot more different types of users to the system, the load tends to be balanced out because not everybody needs the same resource at exactly the same time. As long as the distribution of different resource requirement is relatively even, the larger the system is, the stabler it becomes.

Statistically, adding multiple standard derivations yield a smaller value than their sum.

[shykes]

No, that's the theoretical beauty of aggregation. If black friday causes a 10x spike in transactions, a larger system won't help you.

[riobard]

This kind of edge cases will happen much more frequently when you have multiple smaller systems. A larger system helps you by balancing out those. Will a larger system run out of resources if everyone requests it at the same time? Of course it will, but the likelihood will be statistically smaller than smaller systems.